1 Oracle Text SQL Statements and Operators

ALTER INDEX Purpose

Use ALTER INDEX to make changes to, or perform maintenance tasks for a CONTEXT, CTXCAT, or CTXRULE index.

All Index Types

Use ALTER INDEX to perform the following tasks on all Oracle Text index types:

• Rename the index or index partition. See "ALTER INDEX RENAME Syntax".

• Rebuild the index using different preferences. Some restrictions apply for the CTXCAT index type. See "ALTER INDEX REBUILD Syntax".

• Add stopwords to the index. See "ALTER INDEX REBUILD Syntax".

• Add or remove a sub_lexer, and remove a stopword or set of stopwords for a given symbol (language or language-independent). See "ALTER INDEX Sub_Lexer Syntax"

CONTEXT and CTXRULE Index Types

Use ALTER INDEX to perform the following tasks on CONTEXT and CTXRULE index types:

• Resume a failed index operation (creation/optimization).

• Add sections and stop sections to the index.

• Replace index metadata.

  See Also:

  "ALTER INDEX REBUILD Syntax" to learn more about performing these tasks

Overview of ALTER INDEX Syntax

The syntax for ALTER INDEX is fairly complex. The major divisions are covered in the following sections:

• "ALTER INDEX MODIFY PARTITION Syntax"—use this to modify an index partition's metadata.

• "ALTER INDEX PARAMETERS Syntax"—use this to modify the parameters of a nonpartitioned index, or to modify all partitions of a local partitioned index, without rebuilding the index.

• "ALTER INDEX RENAME Syntax"—use this to rename an index or index partition.

• "ALTER INDEX REBUILD Syntax"—use this to rebuild an index or index partition. With this statement, you can also replace index metadata; add stopwords, sections, and stop sections to an index; and resume a failed operation.

  The parameters for ALTER INDEX REBUILD have their own syntax, which is a subset of the syntax for ALTER INDEX. For example, the ALTER INDEX REBUILD PARAMETERS statement can take either REPLACE or RESUME as an argument, and ALTER INDEX REBUILD PARAMETERS ('REPLACE') can take several arguments. Valid examples of ALTER INDEX REBUILD include the following statements:

  ALTER INDEX REBUILD PARALLEL n
  ALTER INDEX REBUILD PARAMETERS ('SYNC memsize')
  ALTER INDEX REBUILD PARAMETERS ('REPLACE DATASTORE datastore_pref')
  ALTER INDEX REBUILD PARAMETERS ('REPLACE WORDLIST wordlist_pref')
  

ALTER INDEX MODIFY PARTITION Syntax

Use the following syntax to modify the metadata of an index partition:

ALTER INDEX index_name MODIFY PARTITION partition_name PARAMETER (paramstring)

index_name

Specify the name of the index whose partition metadata you want to modify.

partition_name

Specify the name of the index partition whose metadata you want to modify.

paramstring

The only valid argument here is 'REPLACE METADATA'. This follows the same syntax as ALTER INDEX REBUILD PARTITION PARAMETERS ('REPLACE METADATA'); see the REPLACE METADATA subsection of the "ALTER INDEX REBUILD Syntax" section for more information. (The two statements are equivalent. ALTER INDEX MODIFY PARTITION is offered for ease of use, and is the recommended syntax.)

ALTER INDEX PARAMETERS Syntax

Use the following syntax to modify the parameters either of nonpartitioned or local partitioned indexes, without rebuilding the index. For partitioned indexes, this statement works at the index level, not at the partition level. This statement changes information for the entire index, including all partitions.

ALTER INDEX index_name PARAMETERS (paramstring)

paramstring

ALTER INDEX PARAMETERS accepts the following arguments for paramstring:

• 'REPLACE METADATA'

  Replaces current metadata. See the REPLACE METADATA subsection of the "ALTER INDEX REBUILD Syntax" section for more information.

• 'ADD STOPWORD'

  Dynamically adds a stopword to an index. See the ADD STOPWORD subsection of the "ALTER INDEX REBUILD Syntax" section for more information.

• 'ADD FIELD SECTION'

  Dynamically adds a field section to an index. See the ADD FIELD subsection of the "ALTER INDEX REBUILD Syntax" section for more information. You can add an unlimited number of field sections.

• 'ADD ZONE SECTION'

  Dynamically adds a zone section to an index. See the ADD ZONE subsection of the "ALTER INDEX REBUILD Syntax" section for more information.

• 'ADD ATTR SECTION'

  Dynamically adds an attribute section to an index. See the ADD ATTR subsection of the "ALTER INDEX REBUILD Syntax" section for more information.

• 'ADD SDATA SECTION'

  Dynamically adds an SDATA section to an index, without rebuilding the index. An SDATA section can only be added to BASIC, HTML, XML, and NEWS section groups. It supports both global as well as local indexes. The syntax is:

  ALTER INDEX index_name PARAMETERS (ADD SDATA SECTION sdata_section_name TAG sdata_section_tag DATATYPE sdata_section_datatype);
  

  The datatype can be VARCHAR2, CHAR, NUMBER, DATE, or RAW.

  See "Adding an SDATA Section" for more information.

Each of the above described parameters has an equivalent ALTER INDEX REBUILD PARAMETERS version, except ADD SDATA SECTION.

For example, ALTER INDEX PARAMETERS ('REPLACE METADATA') is equivalent to ALTER INDEX REBUILD PARAMETERS ('REPLACE METADATA'). However, the ALTER INDEX PARAMETERS versions work on either partitioned or nonpartitioned indexes, whereas the ALTER INDEX REBUILD PARAMETERS versions work only on nonpartitioned indexes.

ALTER INDEX RENAME Syntax

Use the following syntax to rename an index or index partition:

ALTER INDEX [schema.]index_name RENAME TO new_index_name;  

ALTER INDEX [schema.]index_name RENAME PARTITION part_name TO new_part_name;

[schema.]index_name

Specify the name of the index to rename.

new_index_name

Specify the new name for schema.index. The new_index_name parameter can be no more than 25 bytes, and 21 bytes for a partitioned index. If you specify a name longer than 25 bytes (or longer than 21 bytes for a partitioned index), then Oracle Text returns an error and the renamed index is no longer valid.

Note:

When new_index_name is more than 25 bytes (21 for local partitioned index) and less than 30 bytes, Oracle Text renames the index, even though the system returns an error. To drop the index and associated tables, you must drop new_index_name with the DROP INDEX statement and then re-create and drop index_name.

part_name

Specify the name of the index partition to rename.

new_part_name

Specify the new name for partition.

ALTER INDEX REBUILD Syntax

Use ALTER INDEX REBUILD to rebuild an index, rebuild an index partition, resume a failed operation, replace index metadata, add stopwords to an index, or add sections and stop sections to an index.

The ALTER INDEX REBUILD syntax has its own subsyntax. That is, its parameters have their own syntax. For example, the ALTER INDEX REBUILD PARAMETERS statement can take either REPLACE or RESUME as an argument, and ALTER INDEX REBUILD PARAMETERS ('REPLACE') has several arguments it can take.

Valid examples of ALTER INDEX REBUILD include the following statements:

ALTER INDEX REBUILD PARALLEL n
ALTER INDEX REBUILD PARAMETERS (SYNC memsize)
ALTER INDEX REBUILD PARAMETERS (REPLACE DATASTORE datastore_pref)
ALTER INDEX REBUILD PARAMETERS (REPLACE WORDLIST wordlist_pref)

This is the syntax for ALTER INDEX REBUILD:

ALTER INDEX [schema.]index [REBUILD] [PARTITION partname] [ONLINE] [PARAMETERS
(paramstring)][PARALLEL N];

PARTITION partname

Rebuilds the index partition partname. Only one index partition can be built at a time.

When you rebuild a partition you can specify only RESUME or REPLACE in paramstring. These operations work only on the partname you specify.

With the REPLACE operation, you can specify MEMORY, STORAGE, and SYNC for each index partition.

Adding Partitions To add a partition to the base table, use the ALTER TABLE SQL statement. When you add a partition to an indexed table, Oracle Text automatically creates the metadata for the new index partition. The new index partition has the same name as the new table partition. Change the index partition name with ALTER INDEX RENAME.

Splitting or Merging Partitions Splitting or merging a table partition with ALTER TABLE renders the index partitions invalid. You must rebuild them with ALTER INDEX REBUILD.

ONLINE

Enables you to continue to perform updates, insertions, and deletions on a base table. It does not enable you to query the base table. The ONLINE keyword can only be used with the Enteprise Edition of Oracle Database.

Note:

You can specify REPLACE or RESUME when rebuilding an index or an index partition ONLINE.

PARAMETERS (paramstring)

Optionally specify paramstring. If you do not specify paramstring, then Oracle Text rebuilds the index with existing preference settings.

The syntax for paramstring is as follows:

paramstring = 

'REPLACE 
     [DATASTORE datastore_pref] 
     [FILTER filter_pref] 
     [LEXER lexer_pref] 
     [WORDLIST wordlist_pref] 
     [STORAGE storage_pref] 
     [STOPLIST stoplist] 
     [SECTION GROUP section_group]
     [MEMORY memsize
     [[POPULATE | NOPOPULATE]
     [INDEX SET index_set]
 
     [METADATA preference new_preference]
     [METADATA FORMAT COLUMN format_column_name]
     [[METADATA] SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)]
     [[METADATA] TRANSACTIONAL|NONTRANSACTIONAL

| RESUME [memory memsize]
| OPTIMIZE [token index_token | fast | full [maxtime (time | unlimited)]
| SYNC [memory memsize]
| ADD STOPWORD word [language language]
| ADD ZONE SECTION section_name tag tag
| ADD FIELD SECTION section_name tag tag [(VISIBLE | INVISIBLE)]
| ADD ATTR SECTION section_name tag tag@attr
| ADD STOP SECTION tag'

REPLACE [optional_preference_list]

Rebuilds an index. You can optionally specify your own preferences, or system-defined preferences.

You can replace only preferences that are supported for that index type. For instance, you cannot replace index set for a CONTEXT or CTXRULE index. Similarly, for the CTXCAT index type, you can replace lexer, wordlist, storage index set, and memory preferences.

The POPULATE parameter is the default and need not be specified. If you want to empty the index of its contents, then specify NOPOPULATE. Clear an index of its contents when you must rebuild your index incrementally. The NOPOPULATE choice is available for a specific partition of the index, and not just for the entire index.

If you are rebuilding a partitioned index using the REPLACE parameter, then you can specify only STORAGE, MEMORY, and NOPOPULATE.

A new wordlist preference SEPARATE_OFFSETS specifies that the token_info in the index is stored as docids only in one place, and offsets is stored only in another place. Refer to Oracle Text Application Developer's Guide for information on improved response time using the SEPARATE_OFFSETS option of CONTEXT index.

Note:

If this procedure modifies the existing index tables for only the following storage attributes of the BASIC_STORAGE type (any one of them), then it will not result in re-indexing of data:

• BIG_IO

• I_INDEX_CLAUSE

• I_TABLE_CLAUSE

• SEPARATE_OFFSETS

See Also:

.

• Chapter 2, "Oracle Text Indexing Elements" for more information about creating and setting preferences, including information about system-defined preferences

• Oracle Text Application Developer's Guide for information on improved response time using the SEPARATE_OFFSETS option of CONTEXT index

REPLACE METADATA preference new_preference

Replaces the existing preference class settings, including SYNC parameters, of the index with the settings from new_preference. Only index preferences and attributes are replaced. The index is not rebuilt.

This statement is useful when you want to replace a preference and its attribute settings after the index is built, without re-indexing all data. re-indexing data can require significant time and computing resources.

This statement is also useful for changing the SYNC parameter type, which can be automatic, manual, or on-commit.

The ALTER INDEX REBUILD PARAMETER ('REPLACE METADATA') statement does not work for a local partitioned index at the global level for the index. You cannot, for example, use this syntax to change a global preference, such as filter or lexer type, without rebuilding the index. Use ALTER INDEX PARAMETERS instead to change the metadata of an index at the global level, including all partitions. See "ALTER INDEX PARAMETERS Syntax".

When should I use the METADATA keyword? REPLACE METADATA should be used only when the change in index metadata will not lead to an inconsistent index, which can lead to incorrect query results.

For example, use this statement in the following instances:

• To go from a single-language lexer to a multilexer in anticipation of multilingual data. For an example, see "Replacing Index Metadata: Changing Single-Lexer to Multilexer".

• To change the WILDCARD_MAXTERMS setting in BASIC_WORDLIST.

• To change the SYNC parameter type, which can be automatic, manual, or on-commit.

These changes are safe and will not lead to an inconsistent index that might adversely affect your query results.

Caution:

The REPLACE METADATA statement can result in inconsistent index data, which can lead to incorrect query results. As such, Oracle does not recommend using this statement, unless you carefully consider the effect it will have on the consistency of your index data and subsequent queries.

There can be many instances when changing metadata can result in inconsistent index data. For example, Oracle recommends against using the METADATA keyword after performing the following procedures:

• Changing the USER_DATASTORE procedure to a new PL/SQL stored procedure that has different output.

• Changing the BASIC_WORDLIST attribute PREFIX_INDEX from NO to YES because no prefixes have been generated for existing documents. Changing it from YES to NO is safe.

• Adding or changing BASIC_LEXER printjoin and skipjoin characters, because new queries with these characters would be lexed differently from how these characters were lexed at index time.

• Do not use REPLACE METADATA with FORWARD_INDEX. Instead use REPLACE STORAGE.

In these unsafe cases, Oracle recommends rebuilding the index.

REPLACE [METADATA] SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)

Specifies SYNC for automatic synchronization of the CONTEXT index when a DML change has occurred to the base table. You can specify one of the SYNC methods shown in Table 1-1.

Table 1-1 ALTER INDEX SYNC Methods

SYNC Type	Description
MANUAL	Means no automatic synchronization. This is the default. You must manually synchronize the index using CTX_DDL.SYNC_INDEX. Use MANUAL to disable ON COMMIT and EVERY synchronization.
EVERY interval-string	Automatically synchronize the index at a regular interval specified by the value of interval-string, which takes the same syntax as that for scheduler jobs. Automatic synchronization using EVERY requires that the index creator have CREATE JOB privileges. Ensure that interval-string is set to a long enough period so that any previous synchronization jobs will have completed. Otherwise, the synchronization job may hang. The interval-string argument must be enclosed in double quotation marks ('' ''). See "Enabling Automatic Index Synchronization" for an example of automatic synchronization syntax.
ON COMMIT	Synchronize the index immediately after a commit. The commit does not return until the sync is complete. (Because the synchronization is performed as a separate transaction, there may be a time period, usually small, when the data is committed but index changes are not.) The operation uses the memory specified with the memory parameter. Note that the sync operation has its own transaction context. If this operation fails, the data transaction still commits. Index synchronization errors are logged in the CTX_USER_INDEX_ERRORS view. See "Viewing Index Errors" under CREATE INDEX. ON COMMIT sync works best when the STAGE_ITAB index option is enabled, because otherwise it causes significant fragmentation of the main index, requiring frequent OPTIMIZE calls. See "Enabling Automatic Index Synchronization" for an example of ON COMMIT syntax. Refer to Oracle Text Application Developer's Guide for more information about the STAGE_ITAB option of the CONTEXT index.

Each partition of a locally partitioned index can have its own type of sync: (ON COMMIT, EVERY, or MANUAL). The type of sync specified in master parameter strings applies to all index partitions unless a partition specifies its own type.

With automatic (EVERY) synchronization, you can specify memory size and parallel synchronization. The syntax is:

... EVERY interval_string MEMORY mem_size PARALLEL paradegree ...

ON COMMIT synchronizations can only be executed serially and at the same memory size as what was specified at index creation.

Note:

This command rebuilds the index. When you want to change the SYNC setting without rebuilding the index, use the REBUILD REPLACE METADATA SYNC (MANUAL | ON COMMIT) operation.

REPLACE [METADATA] TRANSACTIONAL | NONTRANSACTIONAL

This parameter enables you to turn the TRANSACTIONAL property on or off. For more information, see "TRANSACTIONAL".

Using this parameter only succeeds if there are no rows in the DML pending queue. Therefore, you may need to sync the index before issuing this command.

To turn on the TRANSACTIONAL index property:

ALTER INDEX myidx REBUILD PARAMETERS('replace metadata transactional');

or

ALTER INDEX myidx REBUILD PARAMETERS('replace  transactional');

To turn off the TRANSACTIONAL index property:

ALTER INDEX myidx REBUILD PARAMETERS('replace metadata nontransactional');

or

ALTER INDEX myidx REBUILD PARAMETERS('replace  nontransactional');

RESUME [MEMORY memsize]

Resumes a failed index operation. You can optionally specify the amount of memory to use with memsize.

Note:

This ALTER INDEX operation applies only to CONTEXT and CTXRULE indexes. It does not apply to CTXCAT indexes.

ADD STOPWORD word [language language]

Dynamically adds a stopword word to the index.

Index entries for word that existed before this operation are not deleted. However, subsequent queries on word are treated as though it has always been a stopword.

When your stoplist is a multilanguage stoplist, you must specify language.

The index is not rebuilt by this statement.

ADD ZONE SECTION section_name tag tag

Dynamically adds the zone section section_name identified by tag to the existing index.

The added section section_name applies only to documents indexed after this operation. For the change to take effect, you must manually re-index any existing documents that contain the tag.

The index is not rebuilt by this statement.

Note:

This ALTER INDEX operation applies only to CONTEXT and CTXRULE indexes. It does not apply to CTXCAT indexes.

See Also:

"Notes"

ADD FIELD SECTION section_name tag tag [(VISIBLE | INVISIBLE)]

Dynamically adds the field section section_name identified by tag to the existing index. There is no limit to the number of field sections that can be added.

Optionally specify VISIBLE to make the field sections visible. The default is INVISIBLE.

See Also:

CTX_DDL.ADD_FIELD_SECTION for more information on visible and invisible field sections

The added section section_name applies only to documents indexed after this operation. For the change to affect previously indexed documents, you must explicitly re-index the documents that contain the tag.

This statement does not rebuild the index.

Note:

This ALTER INDEX operation applies only to CONTEXT CTXRULE indexes. It does not apply to CTXCAT indexes.

See Also:

"Notes"

ADD ATTR SECTION section_name tag tag@attr

Dynamically adds an attribute section section_name to the existing index. You must specify the XML tag and attribute in the form tag@attr. You can add attribute sections only to XML section groups.

The added attribute section section_name applies only to documents indexed after this operation. For the change to take effect, you must manually re-index any existing documents that contain the tag.

The index is not rebuilt by this statement.

Note:

This ALTER INDEX operation applies only to CONTEXT CTXRULE indexes. It does not apply to CTXCAT indexes.

See Also:

"Notes"

ADD STOP SECTION tag

Dynamically adds the stop section identified by tag to the existing index. As stop sections apply only to automatic sectioning of XML documents, the index must use the AUTO_SECTION_GROUP section group. The tag you specify must be case sensitive and unique within the automatic section group or else ALTER INDEX raises an error.

The added stop section tag applies only to documents indexed after this operation. For the change to affect previously indexed documents, you must explicitly re-index the documents that contain the tag.

The text within a stop section can always be searched.

The number of stop sections you can add is unlimited.

The index is not rebuilt by this statement.

See Also:

"Notes"

Note:

This ALTER INDEX operation applies only to CONTEXT indexes. It does not apply to CTXCAT indexes.

PARALLEL n

Using n, you can optionally specify the parallel degree for parallel indexing. This parameter is supported only when you use SYNC, REPLACE, and RESUME in paramstring. The actual degree of parallelism might be smaller depending on your resources.

Parallel indexing can speed up indexing when you have large amounts of data to index and when your operating system supports multiple CPUs.

ALTER INDEX Sub_Lexer Syntax

Use the following syntax.

New paramstring = 
'REPLACE 
     [DATASTORE datastore_pref] 
     [FILTER filter_pref] 
     [LEXER lexer_pref] 
     [WORDLIST wordlist_pref] 
     [STORAGE storage_pref] 
     [STOPLIST stoplist] 
     [SECTION GROUP section_group]
     [MEMORY memsize
     [[POPULATE | NOPOPULATE]
     [INDEX SET index_set]
 
     [METADATA preference new_preference]
     [[METADATA] SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)]
     [[METADATA] TRANSACTIONAL|NONTRANSACTIONAL
 
| RESUME [memory memsize]
| OPTIMIZE [token index_token | fast | full [maxtime (time | unlimited)]
| SYNC [memory memsize]
| ADD STOPWORD word [language language][LANGUAGE_DEPENDENT(TRUE|FALSE)]
| ADD ZONE SECTION section_name tag tag
| ADD FIELD SECTION section_name tag tag [(VISIBLE | INVISIBLE)]
| ADD ATTR SECTION section_name tag tag@attr
| ADD STOP SECTION tag
| ADD SUB_LEXER sub_lexer_name LANGUAGE language [ALT_VALUE alternate_value_for_language] [LANGUAGE_DEPENDENT (TRUE|FALSE)]
| REMOVE SUB_LEXER LANGUAGE language
| REMOVE STOPWORD word [LANGUAGE language]
| REMOVE STOPWORDS FOR LANGUAGE language
| MIGRATE to MULTI_STOPLIST [LANGUAGE COLUMN lang]
| MIGRATE FIELD SECTION field_section_name to [READ ONLY] MDATA
| UPDATE SUB_LEXER LANGUAGE language TO sub_lexer_preference
| ADD MDATA SECTION secname TAG sectag

Sub_Lexer Example

ALTER INDEX myidx PARAMETERS('ADD SUB_LEXER mycompany_lexer LANGUAGE mycompany LANGUAGE_DEPENDENT FALSE');

ALTER INDEX myidx PARAMETERS('REMOVE STOPWORDS FOR LANGUAGE mycompany');

Sub_Lexer Notes

The language can be Oracle predefined language symbols (globalization support name or abbreviation of an Oracle Text-supported language), or user-defined symbols for language independent sub_lexer or stopword.

ADD SUB_LEXER

The following conditions apply:

• If LANGUAGE_DEPENDENT clause is not provided, it will default TRUE.

• Sync will be blocked (or it will be blocked by sync).

• If adding first language independent sub_lexer, then base table will also be locked.

• Adding first language independent sub_lexer or stopword will take longer to complete. Otherwise, it should take fraction of a second to complete unless it's being blocked by ongoing sync process on the same index.

ALTER INDEX Examples

Resuming Failed Index

The following statement resumes the indexing operation on newsindex with 2 megabytes of memory:

ALTER INDEX newsindex REBUILD PARAMETERS('resume memory 2M');

Rebuilding an Index

The following statement rebuilds the index, replacing the stoplist preference with new_stop.

ALTER INDEX newsindex REBUILD PARAMETERS('replace stoplist new_stop');

Rebuilding a Partitioned Index

The following example creates a partitioned text table, populates it, and creates a partitioned index. It then adds a new partition to the table and rebuilds the index with ALTER INDEX as follows:

PROMPT create partitioned table and populate it

create table part_tab (a int, b varchar2(40)) partition by range(a)
(partition p_tab1 values less than (10),
 partition p_tab2 values less than (20),
 partition p_tab3 values less than (30));

insert into part_tab values (1,'Actinidia deliciosa');
insert into part_tab values (8,'Distictis buccinatoria');
insert into part_tab values (12,'Actinidia quinata');
insert into part_tab values (18,'Distictis Rivers');
insert into part_tab values (21,'pandorea jasminoides Lady Di');
insert into part_tab values (28,'pandorea rosea');

commit;

PROMPT create partitioned index
create index part_idx on part_tab(b) indextype is ctxsys.context
local (partition p_idx1, partition p_idx2, partition p_idx3);

PROMPT add a partition and populate it
alter table part_tab add partition p_tab4 values less than (40);
insert into part_tab values (32, 'passiflora citrina');
insert into part_tab values (33, 'passiflora alatocaerulea');
commit;

The following statement rebuilds the index in the newly populated partition. In general, the index partition name for a newly added partition is the same as the table partition name, unless the name has already been used. In this case, Oracle Text generates a new name.

alter index part_idx rebuild partition p_tab4;

The following statement queries the table for the two hits in the newly added partition:

select * from part_tab where contains(b,'passiflora') >0;

The following statement queries the newly added partition directly:

select * from part_tab partition (p_tab4) where contains(b,'passiflora') >;

Replacing Index Metadata: Changing Single-Lexer to Multilexer

The following example demonstrates how an application can migrate from single-language documents (English) to multilanguage documents (English and Spanish) by replacing the index metadata for the lexer.

REM creates a simple table, which stores only English (American) text

create table simple (text varchar2(80));
insert into simple values ('the quick brown fox');
commit;

REM create a simple lexer to lex this English text

begin
  ctx_ddl.create_preference('us_lexer','basic_lexer');
end;
/

REM create a text index on the simple table
create index simple_idx on simple(text)
indextype is ctxsys.context parameters ('lexer us_lexer');

REM we can query easily
select * from simple where contains(text, 'fox')>0;

REM now suppose we want to start accepting Spanish documents.
REM first we have to extend the table with a language column
alter table simple add (lang varchar2(10) default 'us');

REM now let's create a Spanish lexer, 
begin
  ctx_ddl.create_preference('e_lexer','basic_lexer');
  ctx_ddl.set_attribute('e_lexer','base_letter','yes');
end;
/
REM Then create a multilexer incorporating our English and Spanish lexers.
REM Note that the DEFAULT lexer is the exact same lexer, with which we have
REM have already indexed all the documents.
begin
  ctx_ddl.create_preference('m_lexer','multi_lexer');
  ctx_ddl.add_sub_lexer('m_lexer','default','us_lexer');
  ctx_ddl.add_sub_lexer('m_lexer','spanish','e_lexer');
end;
/
REM next replace our metadata
alter index simple_idx rebuild
parameters ('replace metadata language column lang lexer m_lexer');

REM We are ready for some Spanish data.  Note that we could have inserted
REM this BEFORE the alter index, as long as we did not SYNC.
insert into simple values ('el zorro marrón rápido', 'e');
commit;
exec ctx_ddl.sync_index('simple_idx');
REM now query the Spanish data with base lettering:
select * from simple where contains(text, 'rapido')>0;

Optimizing the Index

To optimize your index, use CTX_DDL.OPTIMIZE_INDEX.

Synchronizing the Index

To synchronize your index, use CTX_DDL.SYNC_INDEX.

Adding a Zone Section

To add to the index the zone section author identified by the tag <author>, enter the following statement:

ALTER INDEX myindex REBUILD PARAMETERS('add zone section author tag author');

Adding a Stop Section

To add a stop section identified by tag <fluff> to the index that uses the AUTO_SECTION_GROUP, enter the following statement:

ALTER INDEX myindex REBUILD PARAMETERS('add stop section fluff');

Adding an Attribute Section

Assume that the following text appears in an XML document:

<book title="Tale of Two Cities">It was the best of times.</book>

Assume also that you want to create a separate section for the title attribute and you want to name the new attribute section booktitle. To do so, enter the following statement:

ALTER INDEX myindex REBUILD PARAMETERS('add attr section booktitle tag
title@book');

Adding an SDATA Section

To add an SDATA section S1 of NUMBER data type and identified by tag T1, to the index, enter the following statement:

ALTER INDEX myindex PARAMETERS('add sdata section S1 tag T1 datatype NUMBER);

Using Flashback Queries

If a Text query is flashed back to a point before an ALTER INDEX statement was issued on the Text index for which the query is being run, then:

• The query optimizer will not choose the index access path for that given index because the index is treated according to its creation time with ALTER INDEX. Therefore, to the query optimizer, the index is perceived not to exist.

• The functional processing of the Text operator will fail with ORA-01466 or ORA-08176 errors if the ALTER INDEX statement involves re-creation of DR$ index tables.

To work around this issue, use the DBMS_FLASHBACK package. For example:

EXEC dbms_flashback.enable_at_system_change_number(:scn);
SELECT id from documents WHERE CONTAINS(text, 'oracle')>0;
EXEC dbms_flashback.disable;

Notes

Add Section Constraints

Before altering the index section information, Oracle Text checks the new section against the existing sections to ensure that all validity constraints are met. These constraints are the same for adding a section to a section group with the CTX_DDL PL/SQL package and are as follows:

• You cannot add zone, field, or stop sections to a NULL_SECTION_GROUP.

• You cannot add zone, field, or attribute sections to an automatic section group.

• You cannot add attribute sections to anything other than XML section groups.

• You cannot have the same tag for two different sections.

• Section names for zone, field, and attribute sections cannot intersect.

• You cannot exceed 64 fields per section.

• You cannot add stop sections to basic, HTML, XML, or news section groups.

• SENTENCE and PARAGRAPH are reserved section names.

Related Topics

CTX_DDL.SYNC_INDEX in Chapter 8, "CTX_DDL Package"

CTX_DDL.OPTIMIZE_INDEX in Chapter 8, "CTX_DDL Package"

CREATE INDEX

Purpose

Use the ALTER TABLE statement to add, modify, split, merge, exchange, or drop a partitioned text table with a context domain index. The following sections describe some of the ALTER TABLE operations.

Modify Partition Syntax

Unusable Local Indexes

ALTER TABLE  [schema.]table MODIFY PARTITION partition UNUSABLE LOCAL INDEXES

Marks the index partition corresponding to the given table partition UNUSABLE. You might mark an index partition unusable before you rebuild the index partition as described in "Rebuild Unusable Local Indexes".

If the index partition is not marked unusable, then the statement returns without actually rebuilding the local index partition.

Rebuild Unusable Local Indexes

ALTER TABLE  [schema.]table MODIFY PARTITION partition REBUILD UNUSABLE LOCAL
INDEXES

Rebuilds the index partition corresponding to the specified table partition that has an UNUSABLE status.

Add Partition Syntax

ALTER TABLE [schema.]table ADD PARTITION [partition] 
VALUES LESS THAN (value_list) [partition_description]

Adds a new partition to the high end of a range-partitioned table.

To add a partition to the beginning or to the middle of the table, use the ALTER TABLE SPLIT PARTITION statement.

The newly added table partition is always empty, and the context domain index (if any) status for this partition is always VALID. After issuing DML, if you want to synchronize or optimize this newly added index partition, then you must look up the index partition name and enter the ALTER INDEX REBUILD PARTITION statement. For this newly added partition, the index partition name is usually the same as the table partition name, but if the table partition name is already used by another index partition, the system assigns a name in the form of SYS_Pn.

By querying the USER_IND_PARTITIONS view and comparing the HIGH_VALUE field, you can determine the index partition name for the newly added partition.

Merge Partition Syntax

ALTER TABLE [schema.]table 
MERGE PARTITIONS partition1, partition2 
[INTO PARTITION [new_partition] [partition_description]]
[UPDATE GLOBAL INDEXES]

Applies only to a range partition. This statement merges the contents of two adjacent partitions into a new partition and then drops the original two partitions. If the resulting partition is non-empty, then the corresponding local domain index partition is marked UNUSABLE. You can use ALTER TABLE MODIFY PARTITION to rebuild the partition index.

For a global, nonpartitioned index, if you perform the merge operation without an UPDATE GLOBAL INDEXES clause, then the resulting index (if not NULL) will be invalid and must be rebuilt. If you specify the UPDATE GLOBAL INDEXES clause after the operation and the SYNC type is MANUAL, then the index will be valid, but you still must synchronize the index with CTX_DDL.SYNC_INDEX for the update to take place.

The naming convention for the resulting index partition is the same as in the ALTER TABLE ADD PARTITION statement.

Split Partition Syntax

ALTER TABLE [schema.]table
SPLIT PARTITION partition_name_old 
AT (value_list)
[into (partition_description, partition_description)]
[parallel_clause]
[UPDATE GLOBAL INDEXES]

Applies only to range partitions. This statement divides a table partition into two partitions, thus adding a new partition to the table. The local corresponding index partitions will be marked UNUSABLE if the corresponding table partitions are non-empty. Use the ALTER TABLE MODIFY PARTITION statement to rebuild the partition indexes.

For a global, nonpartitioned index, if you perform the split operation without an UPDATE GLOBAL INDEXES clause, then the resulting index (if not NULL) will be invalid and must be rebuilt. If you specify the UPDATE GLOBAL INDEXES clause after the operation and the SYNC type is MANUAL, then the index will be valid, but you still must synchronize the index with CTX_DDL.SYNC_INDEX for the update to take place.

The naming convention for the two resulting index partition is the same as in the ALTER TABLE ADD PARTITION statement.

Exchange Partition Syntax

ALTER TABLE [schema.]table EXCHANGE PARTITION partition WITH TABLE table
[INCLUDING|EXCLUDING INDEXES}
[WITH|WITHOUT VALIDATION]
[EXCEPTIONS INTO [schema.]table]
[UPDATE GLOBAL INDEXES]

Converts a partition to a nonpartitioned table, and converts a table to a partition of a partitioned table by exchanging their data segments. Rowids are preserved.

If EXCLUDING INDEXES is specified, all the context indexes corresponding to the partition and all the indexes on the exchanged table are marked as UNUSABLE. To rebuild the new index partition in this case, issue an ALTER TABLE MODIFY PARTITION statement.

If INCLUDING INDEXES is specified, then for every local domain index on the partitioned table, there must be a nonpartitioned domain index on the nonpartitioned table. The local index partitions are exchanged with the corresponding regular indexes.

For a global, nonpartitioned index, if you perform the exchange operation without an UPDATE GLOBAL INDEXES clause, then the resulting index (if not NULL) will be invalid and must be rebuilt. If you specify the UPDATE GLOBAL INDEXES clause after the operation and the SYNC type is MANUAL, then the index will be valid, but you still must synchronize the index with CTX_DDL.SYNC_INDEX for the update to take place.

Field Sections

Field section queries might not work the same way if the nonpartitioned index and local index use different section IDs for the same field section.

Storage

Storage is not changed. So if the index on the nonpartitioned table $I table was in tablespace XYZ, then after the exchange partition, it will still be in tablespace XYZ, but now it is the $I table for an index partition.

Storage preferences are not switched, so if you switch and then rebuild the index, then the table may be created in a different location.

Restrictions

Both indexes must be equivalent. They must use the same objects and the same settings for each object. Note that Oracle Text checks only that the indexes are using the same object. But they should use the same exact everything.

No index object can be partitioned, that is, when the user has used the storage object to partition the $I, $N tables.

If either index or index partition does not meet all these restrictions an error is raised and both the index and index partition will be INVALID. You must manually rebuild both index and index partition using the ALTER INDEX REBUILD statement.

Truncate Partition Syntax

ALTER TABLE [schema.]table TRUNCATE PARTITION [DROP|REUSE STORAGE] [UPDATE GLOBAL
INDEXES]

Removes all rows from a partition in a table. Corresponding CONTEXT index partitions are also removed.

For a global, nonpartitioned index, if you perform the truncate operation without an UPDATE GLOBAL INDEXES clause, then the resulting index (if not NULL) will be invalid and must be rebuilt. If you specify the UPDATE GLOBAL INDEXES clause after the operation, the index will be valid.

ALTER TABLE Examples

Global Index on Partitioned Table Examples

The following example creates a range-partitioned table with three partitions. Each partition is populated with two rows. A global, nonpartitioned CONTEXT index is then created. To demonstrate the UPDATE GLOBAL INDEXES clause, the partitions are split and merged with an index synchronization.

create table tdrexglb_part(a int, b varchar2(40)) partition by range(a)
(partition p1 values less than (10),
 partition p2 values less than (20),
 partition p3 values less than (30));

insert into tdrexglb_part values (1,'row1');
insert into tdrexglb_part values (8,'row2');
insert into tdrexglb_part values (11,'row11');
insert into tdrexglb_part values (18,'row18');
insert into tdrexglb_part values (21,'row21');
insert into tdrexglb_part values (28,'row28');

commit;
create index tdrexglb_parti on tdrexglb_part(b) indextype is ctxsys.context;

create table tdrexglb(a int, b varchar2(40));

insert into tdrexglb values(20,'newrow20');
commit;


PROMPT make sure query works
select * from tdrexglb_part where contains(b,'row18') >0;

PROMPT split partition
alter table tdrexglb_part split partition p2 at (15) into
(partition p21, partition p22) update global indexes;

PROMPT before sync
select * from tdrexglb_part where contains(b,'row11') >0;
select * from tdrexglb_part where contains(b,'row18') >0;

exec ctx_ddl.sync_index('tdrexglb_parti')

PROMPT after sync
select * from tdrexglb_part where contains(b,'row11') >0;
select * from tdrexglb_part where contains(b,'row18') >0;

PROMPT merge partition
alter table tdrexglb_part merge partitions p22, p3 
into partition pnew3 update global indexes;

PROMPT before sync
select * from tdrexglb_part where contains(b,'row18') >0;
select * from tdrexglb_part where contains(b,'row28') >0;
exec ctx_ddl.sync_index('tdrexglb_parti');

PROMPT after sync
select * from tdrexglb_part where contains(b,'row18') >0;
select * from tdrexglb_part where contains(b,'row28') >0;

PROMPT drop partition 
alter table tdrexglb_part drop partition p1 update global indexes;

PROMPT before sync
select * from tdrexglb_part where contains(b,'row1') >0;
exec ctx_ddl.sync_index('tdrexglb_parti');

PROMPT after sync
select * from tdrexglb_part where contains(b,'row1') >0;

PROMPT exchange partition
alter table tdrexglb_part exchange partition pnew3 with table
tdrexglb update global indexes;

PROMPT before sync
select * from tdrexglb_part where contains(b,'newrow20') >0;
select * from tdrexglb_part where contains(b,'row28') >0;

exec ctx_ddl.sync_index('tdrexglb_parti');
PROMPT after sync
select * from tdrexglb_part where contains(b,'newrow20') >0;
select * from tdrexglb_part where contains(b,'row28') >0;

PROMPT move table partition
alter table tdrexglb_part move partition p21 update global indexes;
PROMPT before sync
select * from tdrexglb_part where contains(b,'row11') >0;

exec ctx_ddl.sync_index('tdrexglb_parti');
PROMPT after sync
select * from tdrexglb_part where contains(b,'row11') >0;

PROMPT truncate table partition
alter table tdrexglb_part truncate partition p21 update global indexes;

update global indexes;

About Performance

Use the CATSEARCH operator with a CTXCAT index mainly to improve mixed-query performance. Specify your text query condition with text_query and your structured condition with the structured_query argument.

Internally, Oracle Text uses a combined B-tree index on text and structured columns to quickly produce results satisfying the query.

Limitations

If the optimizer chooses to use the functional query invocation, then your query will fail. The optimizer might choose functional invocation when your structured clause is highly selective.

The structured_query argument of the CATSEARCH operator must reference columns used during CREATE INDEX sets; otherwise, error DRG-10845 will be raised. For example, the error will be raised if you issue a CATSEARCH query on a view created on top of a table with the CTXCAT index on it, and the name of the logical column on the view is different from the actual column name on the physical table. The columns referenced by the structured_query argument of the CATSEARCH operator must be the physical column name used during CREATE INDEX sets, not the logical column on the view.

Syntax

CATSEARCH(

[schema.]column,
text_query       [VARCHAR2|CLOB],
structured_query VARCHAR2,

RETURN NUMBER;

[schema.]column

Specifies the text column to be searched on. This column must have a CTXCAT index associated with it.

text_query

Specify one of the following to define your search in column:

• CATSEARCH Query Operations

• Query Template Specification (for using CONTEXT grammar)

CATSEARCH Query Operations

The CATSEARCH operator supports only the following query operations:

• Logical AND

• Logical OR (|)

• Logical NOT (-)

• " " (quoted phrases)

• Wildcarding

Table 1-2 provides the syntax for these operators.

The following limitations apply to these operators:

• The left-hand side (the column name) must be a column named in at least one of the indexes of the index set.

• The left-hand side must be a plain column name. Functions and expressions are not allowed.

• The right-hand side must be composed of literal values. Functions, expressions, other columns, and subselects are not allowed.

• Multiple criteria can be combined with AND. Note that OR is not supported.

• When querying a remote table through a database link, the database link must be specified for CATSEARCH as well as for the table being queried.

For example, these expressions are supported:

catsearch(text, 'dog', 'foo > 15')
catsearch(text, 'dog', 'bar = ''SMITH''')
catsearch(text, 'dog', 'foo between 1 and 15')
catsearch(text, 'dog', 'foo = 1 and abc = 123')
catsearch@remote(text, 'dog', 'foo = 1 and abc = 123')

These expressions are not supported:

catsearch(text, 'dog', 'upper(bar) = ''A''')
catsearch(text, 'dog', 'bar LIKE ''A%''')
catsearch(text, 'dog', 'foo = abc')
catsearch(text, 'dog', 'foo = 1 or abc = 3')

Query Template Specification

Specifies a marked-up string that specifies a query template. Specify one of the following templates:

• Query rewrite, used to expand a query string into different versions

• Progressive relaxation, used to progressively enter less restrictive versions of a query to increase recall

• Alternate grammar, used to specify CONTAINS operators (See "CONTEXT Query Grammar Examples")

• Alternate language, used to specify alternate query language

• Alternate scoring, used to specify alternate scoring algorithms

  See Also:

  The text_query parameter description for CONTAINS for more information about the syntax for these query templates

structured_query

Specifies the structured conditions and the ORDER BY clause. There must exist an index for any column you specify. For example, if you specify 'category_id=1 order by bid_close', you must have an index for 'category_id, bid_close' as specified with the CTX_DDL.ADD_INDEX package.

With structured_query, you can use standard SQL syntax only with the following operators:

• =

• <=

• >=

• >

• <

• IN

• BETWEEN

• AND (to combine two or more clauses)

  Note:

  You cannot use parentheses () in the structured_query parameter.

Examples

1. Create the table.

   The following statement creates the table to be indexed:

   CREATE TABLE auction (category_id number primary key, title varchar2(20), 
   bid_close date);
   

   The following statements insert the values into the table:

   INSERT INTO auction values(1, 'Sony DVD Player', '20-FEB-2012');
   INSERT INTO auction values(2, 'Sony DVD Player', '24-FEB-2012');
   INSERT INTO auction values(3, 'Pioneer DVD Player', '25-FEB-2012');
   INSERT INTO auction values(4, 'Sony DVD Player', '25-FEB-2012');
   INSERT INTO auction values(5, 'Bose Speaker', '22-FEB-2012');
   INSERT INTO auction values(6, 'Tascam CD Burner', '25-FEB-2012');
   INSERT INTO auction values(7, 'Nikon digital camera', '22-FEB-2012');
   INSERT INTO auction values(8, 'Canon digital camera', '26-FEB-2012');
   

2. Create the CTXCAT index.

   The following statements create the CTXCAT index:

   begin
   

   ctx_ddl.create_index_set('auction_iset');
   ctx_ddl.add_index('auction_iset','bid_close'); 
   

   end;
   /
   CREATE INDEX auction_titlex ON auction(title) INDEXTYPE IS CTXSYS.CTXCAT
   PARAMETERS ('index set auction_iset');
   

3. Query the table.

   A typical query with CATSEARCH might include a structured clause as follows to find all rows that contain the word camera ordered by bid_close:

   SELECT * FROM auction WHERE CATSEARCH(title, 'camera', 'order by bid_close desc')>
   0;
   
   CATEGORY_ID TITLE                BID_CLOSE
   ----------- -------------------- ---------
             8 Canon digital camera 26-FEB-12
             7 Nikon digital camera 22-FEB-12
   

   The following query finds all rows that contain the phrase Sony DVD Player and that have a bid close date of February 20, 2012:

   SELECT * FROM auction WHERE CATSEARCH(title, '"Sony DVD Player"',
   'bid_close=''20-FEB-00''')> 0;
    
   CATEGORY_ID TITLE                BID_CLOSE
   ----------- -------------------- ---------
             1 Sony DVD Player       20-FEB-12
   

   The following query finds all rows with the terms Sony and DVD and Player:

   SELECT * FROM auction WHERE CATSEARCH(title, 'Sony DVD Player', 
   'order by bid_close
   desc')> 0;
   CATEGORY_ID TITLE                BID_CLOSE
   ----------- -------------------- ---------
             4 Sony DVD Player       25-FEB-12
             2 Sony DVD Player       24-FEB-12
             1 Sony DVD Player       20-FEB-12
   

   The following query finds all rows with the term DVD and not Player:

   SELECT * FROM auction WHERE CATSEARCH(title, 'DVD - Player', 'order by bid_close
   desc')> 0;
    
   CATEGORY_ID TITLE                BID_CLOSE
   ----------- -------------------- ---------
             6 Tascam CD Burner     25-FEB-12
   

   The following query finds all rows with the terms CD or DVD or Speaker:

   SELECT * FROM auction WHERE CATSEARCH(title, 'CD | DVD | Speaker', 'order by
   bid_close desc')> 0;
    
   CATEGORY_ID TITLE                BID_CLOSE
   ----------- -------------------- ---------
             3 Pioneer DVD Player   25-FEB-12
             4 Sony DVD Player      25-FEB-12
             6 Tascam CD Burner     25-FEB-12
             2 Sony DVD Player      24-FEB-12
             5 Bose Speaker         22-FEB-12
             1 Sony DVD Player      20-FEB-12
   

   The following query finds all rows that are about audio equipment:

   SELECT * FROM auction WHERE CATSEARCH(title, 'ABOUT(audio equipment)', 
   NULL)> 0;
   

CONTEXT Query Grammar Examples

The following examples show how to specify the CONTEXT grammar in CATSEARCH queries using the template feature:

PROMPT
PROMPT fuzzy: query = ?test
PROMPT should match all fuzzy variations of test (for example, text)
select pk||' ==> '||text from test 
where catsearch(text,
'<query> 
  <textquery grammar="context">
     ?test
  </textquery>
</query>','')>0
order by pk; 

PROMPT
PROMPT fuzzy: query = !sail
PROMPT should match all soundex variations of bot (for example, sell)
select pk||' ==> '||text from test 
where catsearch(text,
'<query> 
  <textquery grammar="context">
     !sail
  </textquery>
</query>','')>0
order by pk; 

PROMPT
PROMPT theme (ABOUT) query
PROMPT query: about(California)
select pk||' ==> '||text from test 
where catsearch(text,
'<query> 
  <textquery grammar="context">
     about(California)
  </textquery>
</query>','')>0
order by pk; 

The following example shows a field section search against a CTXCAT index using CONTEXT grammar by means of a query template in a CATSEARCH query:

-- Create and populate table
create table BOOKS (ID number, INFO varchar2(200), PUBDATE DATE);
 
insert into BOOKS values(1, '<author>NOAM CHOMSKY</author><subject>CIVIL
   RIGHTS</subject><language>ENGLISH</language><publisher>MIT
  PRESS</publisher>', '01-NOV-2003');
 
insert into BOOKS values(2, '<author>NICANOR PARRA</author><subject>POEMS 
  AND ANTIPOEMS</subject><language>SPANISH</language>
  <publisher>VASQUEZ</publisher>', '01-JAN-2001');
 
insert into BOOKS values(1, '<author>LUC SANTE</author><subject>XML
  DATABASE</subject><language>FRENCH</language><publisher>FREE
  PRESS</publisher>', '15-MAY-2002');
 
commit;
 
-- Create index set and section group
exec ctx_ddl.create_index_set('BOOK_INDEX_SET');
exec ctx_ddl.add_index('BOOKSET','PUBDATE');
 
exec ctx_ddl.create_section_group('BOOK_SECTION_GROUP',
      'BASIC_SECTION_GROUP');
exec ctx_ddl.add_field_section('BOOK_SECTION_GROUP','AUTHOR','AUTHOR');
exec ctx_ddl.add_field_section('BOOK_SECTION_GROUP','SUBJECT','SUBJECT');
exec ctx_ddl.add_field_section('BOOK_SECTION_GROUP','LANGUAGE','LANGUAGE');
exec ctx_ddl.add_field_section('BOOK_SECTION_GROUP','PUBLISHER','PUBLISHER'); 
  
-- Create index
create index books_index on books(info) indextype is ctxsys.ctxcat
  parameters('index set book_index_set section group book_section_group');
 
-- Use the index
-- Note that: even though CTXCAT index can be created with field sections, it
-- cannot be accessed using CTXCAT grammar (default for CATSEARCH).
-- We need to use query template with CONTEXT grammar to access field 
-- sections with CATSEARCH.
 
select  id, info from books
where catsearch(info,
'<query>
      <textquery grammar="context">
              NOAM within author and english within language
      </textquery>
 </query>',
'order by pubdate')>0; 

Related Topics

"Syntax for CTXCAT Index Type"

Oracle Text Application Developer's Guide

Syntax

CONTAINS(
         [schema.]column,
         text_query    [VARCHAR2|CLOB]
         [,label       NUMBER])
RETURN NUMBER;

[schema.]column

Specify the text column to be searched on. This column must have a Text index associated with it.

text_query

Specify one of the following (limited to 4000 bytes for a VARCHAR2 or 64000 bytes for a CLOB):

• The query expression that defines your search in column.

• A marked-up document that specifies a query template.

  Use one of the following query templates:

  • Query Rewrite Template

  • Query Result Set Descriptor Template

  • Query Relaxation Template

  • Alternate Grammar Template

  • Language Independent Template

  • Alternate Language Template

  • Alternative Scoring Template

Query Rewrite Template

Use this template to automatically write different versions of a query before you submit the query to Oracle Text. This is useful when you need to maximize the recall of a user query. For example, you can program your application to expand a single phrase query of 'cat dog' into the following queries:

{cat} {dog}
{cat} ; {dog}
{cat} AND {dog}
{cat} ACCUM {dog}

These queries are submitted as one query and results are returned with no duplication. In this example, the query returns documents that contain the phrase cat dog as well as documents in which cat is near dog, and documents that have cat and dog.

This is done with the following template:

 <query>
   <textquery lang="ENGLISH" grammar="CONTEXT"> cat dog
     <progression>
       <seq><rewrite>transform((TOKENS, "{", "}", " "))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", " ; "))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", "AND"))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", "ACCUM"))</rewrite></seq>
     </progression>
   </textquery>
  <score datatype="INTEGER" algorithm="COUNT"/>
</query>

The operator TRANSFORM is used to specify the rewrite rules and has the following syntax (note that it uses double parentheses). The parameters are described in Table 1-3.

TRANSFORM((terms, prefix, suffix, connector))

Query Result Set Descriptor Template

Use this template to take in a Result Set Descriptor. The element ctx_result_set_descriptor is added to the query template. This enables the CONTAINS query cursor to take in a group count query.

The Result Set Interface document is placed in a public variable in the ctx_query package. (ctx_query.result_set_document.)

The CONTAINS query cursor behavior remains unchanged and the Result Set Document is available right after closing the cursor

For example, the following query of kukui nut returns a result set with the following template.

<query>
   <textquery lang="ENGLISH" grammar="CONTEXT">
     <progression>
       <seq><rewrite>transform((TOKENS, "{", "}", " "))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", " ; "))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", "AND"))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", "ACCUM"))</rewrite></seq>
     </progression>
   </textquery>
  <score datatype="INTEGER" algorithm="COUNT"/>
<ctx_result_set_descriptor> 
<group mvdata="facetlist"/>
    <group_values>
       <value id="2"/>
       <value id="3"/>
       <value id="4"/>
    </group_values>
    <count/>
  </group>
</ctx_result_set_descriptor>
</query>

Query Relaxation Template

Use this template to progressively relax your query. Progressive relaxation is when you increase recall by progressively issuing less restrictive versions of a query, so that your application can return an appropriate number of hits to the user.

For example, the query of black pen can be progressively relaxed to:

black pen
black NEAR pen
black AND pen
black ACCUM pen

This is done with the following template

<query>
   <textquery lang="ENGLISH" grammar="CONTEXT">
     <progression>
       <seq>black pen</seq>
       <seq>black NEAR pen</seq>
       <seq>black AND pen</seq>
       <seq>black ACCUM pen</seq>
     </progression>
   </textquery>
   <score datatype="INTEGER" algorithm="COUNT"/>
</query>

Alternate Grammar Template

Use this template to specify an alternate grammar, such as CONTEXT or CATSEARCH. Specifying an alternate grammar enables you to enter queries using different syntax and operators.

For example, with CATSEARCH, enter ABOUT queries using the CONTEXT grammar. Likewise with CONTAINS, enter logical queries using the simplified CATSEARCH syntax.

The phrase 'dog cat mouse' is interpreted as a phrase in CONTAINS. However, with CATSEARCH, this is equivalent to an AND query of 'dog AND cat AND mouse'. Specify that CONTAINS use the alternate grammar with the following template:

<query> 
  <textquery grammar="CTXCAT">dog cat mouse</textquery>
  <score datatype="integer"/>
</query>

Language Independent Template

Use this template to specify a lexer that uses user-defined symbols (or abbreviations) and does not depend on any language.

The following example specifies that the query take a list of language-independent sublexers.

<query>
      <textquery grammar="CONTEXT" lang="ENGLISH">
            Oracle 
      </textquery>
      <score datatype="INTEGER" algorithm="COUNT"/>
      <sublexers>
            <sublexer_label>  SESSION_LANG   </sublexer_label>
            <sublexer_label>   MAIL   </sublexer_label>
            <sublexer_label> CALENDER </sublexer_label>
      </sublexers>
</query>

The following conditions apply:

• The sublexers element consists of one or more sublexer_label elements.

• Each sublexer_label element contains the symbol for the language independent sub_lexer.

• When the sublexers element is specified, the query will be processed with the stopwords and sub_lexers for each of the symbols specified in the sublexers element, and query will return only the documents indexed by the specified sub_lexers.

• A special reserved symbol called SESSION_LANG can be used for the system to pick a language-dependent sub_lexer based on the language specified in lang attribute of the textquery element in the query template. If lang attribute is not specified, then the lang attribute will be based on session language. Query parsed by the chosen sub_lexer will only return documents indexed by that language-dependent sub_lexer. If both SESSION_LANG and lang attribute are specified, the lang attribute will take priority.

• If sublexers element is specified without SESSION_LANG, then lang attribute of textquery element will be ignored.

• Default Behavior:

  If sublexers element is not present in the query template, then query will be parsed with one language-dependent sub-lexer (if any), which is chosen based on the specified lang attribute value or the session language AND all language independent sub-lexers.

Alternate Language Template

Use this template to specify an alternate language:

<query><textquery lang="french">bon soir</textquery></query>

Alternative Scoring Template

Use this template to specify an alternative scoring algorithm.

The following example specifies that the query use the CONTEXT grammar and return integer scores using the COUNT algorithm. This algorithm returns a score as the number of query occurrences in the document.

<query>        
     <textquery grammar="CONTEXT" lang="english"> mustang  
     </textquery>     
     <score datatype="INTEGER" algorithm="COUNT"/>     
</query>

The following example uses the normalization_expr attribute to add SDATA(price) into the score returned by the query, and uses it as the final score:

<query>
    <textquery grammar="CONTEXT" lang="english">
        DEFINESCORE(dog, RELEVANCE) and  cat
    </textquery>
    <score  algorithm="COUNT"  normalization_expr ="doc_score+ SDATA(price)"/>
</query>

The normalization_expr attribute is used only with the alternate scoring template, and is an arithmetic expression that consists of:

• Arithmetic operators: + - * /. The operator precedence is the same as that for SQL operator precedence.

• Grouping operators: (). Parentheses can be used to alter the precedence of the arithmetic operators.

• Absolute function: ABS(n) returns the absolute value of n; where n is any expression that returns a number.

• Logarithmic function: LOG(n): returns the base-10 logarithmic value of n; where n is any expression that returns a number.

• Predefined components: The doc_score predefined component can be used to return the initial query score of a particular document.

• SDATA component: SDATA(name) returns the value of the SDATA with the specified name as the score.

  • Only SDATA with a NUMBER or DATE data type is allowed. An error is raised otherwise.

  • The sdata string and the SDATA name are case-insensitive.

  • Because an SDATA section value can be NULL, any expression with NULL SDATA section value is evaluated as 0. For example: the normalization_expr "doc_score + SDATA(price)" will be evaluated to 0 if SDATA(price) for a given document has a NULL value.

• Numeric literals: There are any number literal that conforms to the SQL pattern of NUMBER literal and is within the range of the double-precision floating-point (-3.4e38 to 3.4e38).

• Date literals: Date literals must be enclosed with DATE (). Only the following format is allowed: YYYY-MM-DD or YYYY-MM-DD HH24:MI:SS. For example: DATE(2005-11-08).

  Consistent with SQL, if no time is specified, then 00:00:00 is assumed.

The normalization_expr attribute overrides the algorithm attribute. That is, if algorithm is set to COUNT, and the user also specifies normalization_expr, then the score will not be count, but the calculated score based on the normalization_expr.

If the score (either from algorithm = COUNT or normalization_expr = ...) is internally calculated to be greater than 100, then it will be set to 100.

If the query relaxation template is used, the score will be further normalized in such a way that documents returned from higher sequences will always have higher scores than documents returned from sequence(s) below.

DATE Literal Restrictions

Only the minus (-) operator is allowed between date-type data (DATE literals and date-type SDATA). Using other operators will result in an error. Subtracting two date-type data will produce a number (float) that represents the difference in number of days between the two dates. For example, the following expression is allowed:

SDATA(dob) –  DATE(2005-11-08)

The following expression is not allowed:

SDATA(dob) +  DATE(2005-11-08)

The plus (+) and minus (-) operators are allowed between numeric data and date type of data. The number operand is interpreted as the number or fraction of days. For example, the following expression is allowed:

DATE(2005-11-08) + 1        = 9 NOV 2005

The following expression is not allowed:

DATE(2005-11-08)* 3          = ERROR

Template Attribute Values

Table 1-4 gives the possible values for template attributes.

Template Grammar Definition

The query template interface is an XML document. Its grammar is defined with the following XML DTD:

Returns

For each row selected, the CONTAINS operator returns a number between 0 and 100 that indicates how relevant the document row is to the query. The number 0 means that Oracle Text found no matches in the row.

Example

The following example searches for all documents in the text column that contain the word oracle. The score for each row is selected with the SCORE operator using a label of 1:

SELECT SCORE(1), title from newsindex 
    WHERE CONTAINS(text, 'oracle', 1) > 0;

The CONTAINS operator must be followed by an expression such as > 0, which specifies that the score value calculated must be greater than zero for the row to be selected.

When the SCORE operator is called (for example, in a SELECT clause), the CONTAINS clause must reference the score label value as in the following example:

SELECT SCORE(1), title from newsindex 
     WHERE CONTAINS(text, 'oracle', 1) > 0 ORDER BY SCORE(1) DESC;

The following example specifies that the query be parsed using the CATSEARCH grammar:

SELECT id FROM test WHERE CONTAINS (text,
 '<query>
   <textquery lang="ENGLISH" grammar="CATSEARCH">
      cheap pokemon
   </textquery>
   <score datatype="INTEGER"/>
  </query>' ) > 0;

Grammar Template Example

The following example shows how to use the CTXCAT grammar in a CONTAINS query. The example creates a CTXCAT and a CONTEXT index on the same table, and compares the query results.

PROMPT create context and ctxcat indexes, both using theme indexing
PROMPT
create index tdrbqcq101x on test(text) indextype is ctxsys.context
parameters ('lexer theme_lexer');

create index tdrbqcq101cx on test(text) indextype is ctxsys.ctxcat
parameters ('lexer theme_lexer');

PROMPT *****  San Diego             ***********
PROMPT *****  CONTEXT grammar       ***********
PROMPT ** should be interpreted as phrase query **
select pk||' ==> '||text from test 
where contains(text,'San Diego')>0
order by pk;

PROMPT *****  San Diego      ***********
PROMPT *****  CTXCAT grammar ***********
PROMPT ** should be interpreted as AND query  ***
select pk||' ==> '||text from test 
where contains(text,
'<query> 
  <textquery grammar="CTXCAT">San Diego</textquery>
  <score datatype="integer"/>
</query>')>0
order by pk;

PROMPT *****  Hitlist from CTXCAT index ***********
select pk||' ==> '||text from test 
where catsearch(text,'San Diego','')>0
order by pk;

Alternate Scoring Query Template Example

The following query template adds price SDATA section (or SDATA filter-by column) value into the score returned by the query and uses it as the final score:

<query>
      <textquery grammar="CONTEXT" lang="english">
             DEFINESCORE(dog, RELEVANCE) and cat
      </textquery>
      <score algorithm="COUNT" normalization_expr ="doc_score+SDATA(price)"/>
</query>

Query Relaxation Template Example

The following query template defines a query relaxation sequence. The query of black pen is entered in sequence as black pen, then black NEAR pen, then black AND pen, and then black ACCUM pen. Query hits are returned in this sequence with no duplication as long as the application requires results.

select id from docs where CONTAINS (text, '
<query>
   <textquery lang="ENGLISH" grammar="CONTEXT">
     <progression>
       <seq>black pen</seq>
       <seq>black NEAR pen</seq>
       <seq>black AND pen</seq>
       <seq>black ACCUM pen</seq>
     </progression>
   </textquery>
   <score datatype="INTEGER" algorithm="COUNT"/>
</query>')>0;

Query relaxation is most effective when your application requires the top n hits to a query, which you can obtain with the DOMAIN_INDEX_SORT or FIRST_ROWS hint, which is being deprecated, in a PL/SQL cursor.

Query Rewrite Template Example

The following template defines a query rewrite sequence. The query of kukui nut is rewritten as follows:

{kukui} {nut}

{kukui} ; {nut}

{kukui} AND {nut}

{kukui} ACCUM {nut}

select id from docs where CONTAINS (text, '
 <query>
   <textquery lang="ENGLISH" grammar="CONTEXT"> kukui nut
     <progression>
       <seq><rewrite>transform((TOKENS, "{", "}", " "))</rewrite></seq>
       <seq><rewrite>transform((TOKENS, "{", "}", " ; "))</rewrite>/seq>
       <seq><rewrite>transform((TOKENS, "{", "}", "AND"))</rewrite><seq/>
       <seq><rewrite>transform((TOKENS, "{", "}", "ACCUM"))</rewrite><seq/>
     </progression>
   </textquery>
  <score datatype="INTEGER" algorithm="COUNT"/>
</query>')>0;

Order By SDATA Sections Template Example

The following query template defines a query sequence for ordering by SDATA section values using the <order> and <orderkey> elements. The first level of ordering is done on the SDATA section price, which is sorted in the ascending order. The second and third level of ordering is done by the SDATA section pub_date and score, both of which are sorted in the descending order.

select id from docs where CONTAINS (text, '
<query>
   <textquery lang="ENGLISH" grammar="CONTEXT"> Oracle </textquery>
   <score datatype="INTEGER" algorithm="COUNT"/>
   <order>
       <orderkey> SDATA(price) ASC </orderkey>
       <orderkey> SDATA(pub_date) DESC </orderKey>
       <orderkey> Score DESC </orderkey>
   </order>
</query>', 1)>0;

The <orderkey> element value must have the following format:

<orderkey> SDATA(sdata_section_name) | score [DESC|ASC] </orderkey>

The sort order is ascending by default, if not specified as either DESC or ASC.

The <orderkey> element will be ignored in the following cases:

• when the Oracle Cost-Based Optimizer (CBO) pushes the SQL query level ordering into the Text index

• when the CONTAINS() predicate is processed functionally

• when the ordering is already specified by the ORDER BY clause in the SQL query statement

Notes

Querying Multilanguage Tables

With the multilexer preference, you can create indexes from multilanguage tables. At query time, the multilexer examines the session's language setting and uses the sublexer preference for that language to parse the query. If the language setting is not mapped, then the default lexer is used.

When the language setting is mapped, the query is parsed and run as usual. The index contains tokens from multiple languages, so such a query can return documents in several languages.

To limit your query to returning documents of a given language, use a structured clause on the language column.

Query Performance Limitation with a Partitioned Index

Oracle Text supports the CONTEXT indexing and querying of a partitioned text table.

However, for optimal performance when querying a partitioned table with an ORDER BY SCORE clause, query the partition. If you query the entire table and use an ORDER BY SCORE clause, the query might not perform optimally unless you include a range predicate that can limit the query to a single partition.

For example, the following statement queries the partition p_tab4 partition directly:

select * from part_tab partition (p_tab4) where contains(b,'oracle') > 0 ORDER BY
SCORE DESC;

Limitation with Remote Execution of CONTAINS Query

Oracle Text supports the remote execution of the CONTAINS operator, but with some limitations. You can invoke the CONTAINS operator in a remote query only if the query is executed completely in the remote database. You cannot use the CONTAINS operator in a subquery of a query, which causes the query to run partly on the remote database and partly on the local database. Doing so will raise the error "ORA-00949: illegal reference to remote database." However, CONTAINS, when invoked remotely from an inner query might run successfully sometimes if view merging is enabled and possible on this query, as in this case the query will be transformed into a single query and, hence, no error will occur.

For example, the following query is correct:

select id from remtab@rdb 
where contains@rdb(text,'hello') > 0;

Related Topics

"Syntax for CONTEXT Index Type"

Chapter 3, "Oracle Text CONTAINS Query Operators"

"The CONTEXT Grammar" topic in Oracle Text Application Developer's Guide

"SCORE"

Purpose

Use CREATE INDEX to create an Oracle Text index. An Oracle Text index is an Oracle Database domain index or composite domain index of type CONTEXT, CTXCAT, or CTXRULE. A domain index is an application-specific index. A composite domain index (CDI) is an Oracle Text index that not only indexes and processes a specified text column, but also indexes and processes FILTER BY and ORDER BY structured columns, which are specified during index creation.

You must create an appropriate Oracle Text index to enter CONTAINS, CATSEARCH, or MATCHES queries.

You cannot create an Oracle Text index on an index-organized table.

You can create the following types of Oracle Text indexes.

CONTEXT

A CONTEXT index is the basic type of Oracle Text index. This is an index on a text column. A CONTEXT index is useful when your source text consists of many large, coherent documents. Query this index with the CONTAINS operator in the WHERE clause of a SELECT statement. This index requires manual synchronization after DML. See "Syntax for CONTEXT Index Type".

CTXCAT

The CTXCAT index is a combined index on a text column and one or more other columns. The CTXCAT type is typically used to index small documents or text fragments, such as item names, prices, and descriptions found in catalogs. Query this index with the CATSEARCH operator in the WHERE clause of a SELECT statement. This type of index is optimized for mixed queries. This index is transactional, automatically updating itself with DML to the base table. See "Syntax for CTXCAT Index Type".

CTXRULE

A CTXRULE index is used to build a document classification application. The CTXRULE index is an index created on a table of queries or a column containing a set of queries, where the queries serve as rules to define the classification criteria. Query this index with the MATCHES operator in the WHERE clause of a SELECT statement. See "Syntax for CTXRULE Index Type".

Required Privileges

You do not need the CTXAPP role to create an Oracle Text index. If you have Oracle Database grants to create a B-tree index on the text column, you have sufficient privilege to create a text index. The issuing owner, table owner, and index owner can all be different users, which is consistent with Oracle standards for creating regular B-tree indexes.

Syntax for CONTEXT Index Type

Uses a CONTEXT index to create an index on a text column. Query this index with the CONTAINS operator in the WHERE clause of a SELECT statement. This index requires manual synchronization after DML.

CREATE INDEX [schema.]index ON [schema.]table(txt_column)
  INDEXTYPE IS ctxsys.context [ONLINE]
  [FILTER BY filter_column[, filter_column]...]
  [ORDER BY oby_column[desc|asc][, oby_column[desc|asc]]...]
  [LOCAL [PARTITION [partition] [PARAMETERS('paramstring')]]

  [, PARTITION [partition] [PARAMETERS('paramstring')]])]

  [PARAMETERS(paramstring)] [PARALLEL n] [UNUSABLE]];

[schema.]index

Specifies the name of the Text index to create.

[schema.]table(txt_column)

Specifies the name of the table and column to index. txt_column is the name of the domain index column on which the CONTAINS() operator will be invoked.

Your table can optionally contain a primary key if you prefer to identify your rows as such when you use procedures in CTX_DOC. When your table has no primary key, document services identifies your documents by ROWID.

Note:

Primary keys of the following type are supported: NUMBER, VARCHAR2, DATE, CHAR, VARCHAR, and RAW.

The column that you specify must be one of the following types: CHAR, VARCHAR, VARCHAR2, BLOB, CLOB, BFILE, XMLType, or URIType.

The table that you specify can be a partitioned table. If you do not specify the LOCAL clause, then a global, nonpartitioned index is created.

The DATE, NUMBER, and nested table columns cannot be indexed. Object columns also cannot be indexed, but their attributes can be indexed, provided that they are atomic data types.

Attempting to create an index on a Virtual Private Database (VPD) protected table will fail unless one of the following criteria is true:

• The VPD policy is created such that it does not apply to the INDEX statement type.

• The policy function returns a NULL predicate for the current user.

• The user (or index owner) is SYS.

• The user has the EXEMPT ACCESS POLICY privilege.

Indexes on multiple columns are not supported with the CONTEXT index type. You must specify only one column in the column list.

ONLINE

Creates the index while enabling DML insertions/updates/deletions on the base table.

During indexing, Oracle Text enqueues DML requests in a pending queue. At the end of the index creation, Oracle Text locks the base table. During this time, DML is blocked. You must synchronize the index in order for DML changes to be available.

Limitations

The following limitations apply to using ONLINE:

• At the very beginning or very end of the ONLINE process, DML might fail.

• ONLINE is supported for CONTEXT indexes only.

FILTER BY filter_column

This is the structured indexed column on which a range or equality predicate in the WHERE clause of a mixed query will operate. You can specify one or more structured columns for filter_column, on which the relational predicates are expected to be specified along with the CONTAINS() predicate in a query.

The Cost-based Optimizer (CBO) will consider pushing down the structured predicates on these FILTER BY columns with the following relational operators: <, <=, =, >=, >, between, and LIKE (for VARCHAR2).

These columns can only be of CHAR, NUMBER, DATE, VARCHAR2, or RAW type. Additionally, VARCHAR2 and RAW types are supported only if the maximum length is specified and is limited to no more than 249. The ADT attributes of supported types (CHAR, NUMBER, DATE, VARCHAR2, or RAW) are also allowed. An error is raised for all other data types. Expressions, for example, func(cola), and virtual columns are not allowed.

txt_column is allowed in the FILTER BY column list.

DML operations on FILTER BY columns are always transactional.

ORDER BY oby_column

This is the structured indexed column on which a structured ORDER BY mixed query will be based. A list of structured oby_columns can be specified in the ORDER BY clause of a CONTAINS() query.

These columns can only be of CHAR, NUMBER, DATE, VARCHAR2, or RAW type. Additionally, VARCHAR2 and RAW types are supported only if the maximum length is specified and is limited to no more than 249. Expressions, for example, func(cola), and virtual columns are not allowed.

The order of the specified columns matters. The Cost-based Optimizer (CBO) will consider pushing the sort into the composite domain index only if the ORDER BY clause in the text query contains:

• Entire ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement

• Only the prefix of the ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement

• The score followed by the prefix of the ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement

• The score following the prefix of the ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement

The following example illustrates Cost-based Optimizer (CBO) behavior with regard to ORDER BY columns:

CREATE INDEX foox ON foo(D) INDEXTYPE IS CTXSYS.CONTEXT
FILTER BY B, C
ORDER BY A, B desc;

Consider the following query:

SELECT A, SCORE(1) FROM foo WHERE CONTAINS(D, 'oracle',1)>0 
AND C>100 ORDER BY col_list;

Note:

If you set NLS_SORT or NLS_COMP parameters (that is, alter session set NLS_SORT = <some lang>; ), then CBO will not push the sort or related structured predicate into the CDI. This behavior is consistent with regular B-tree indexes.

The Cost-based Optimizer (CBO) will consider pushing the sort into the composite domain index (CDI) if col_list has the following values:

A
A,B
SCORE(1), A
SCORE(1), A, B
A, SCORE(1)
A, B, SCORE(1) 

The CBO will not consider to push the sort into the CDI if col_list has the following values:

B
B,A
SCORE(1), B
B, SCORE(1)
A, B, C
A, B asc (or simply A, B)

(or simply A, B)

• The SCORE followed by the prefix of the ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement.

• The SCORE following the prefix of the ordered ORDER BY columns declared by the ORDER BY clause during the CREATE INDEX statement.

Expressions, for example, func(cola), are not allowed.

txt_column appearing in the ORDER BY column list is allowed.

DML operations on ORDER BY columns are always transactional.

Limitations

The following limitations apply to FILTER BY and ORDER BY:

• A structured column is allowed in FILTER BY and ORDER BY clauses. However, a column that is mapped to MDATA in a FILTER BY clause cannot also appear in the ORDER BY clause. An error will be raised in this case.

• The maximum length for CHAR, VARCHAR2, and RAW columns cannot be greater than 249. Additionally, if the VARCHAR2 or RAW column is mapped to an MDATA column, then the specified maximum length cannot exceed 64 and 32 bytes, respectively. (Note that MDATA does not support CHAR data types. If a FILTER BY column of CHAR data type is mapped to an MDATA section, then an error will be raised during the CREATE INDEX statement.)

• The sum of the numbers for INDEXED_COLUMN, FILTER BY columns, and ORDER BY columns cannot be greater than 32.

Restrictions on exporting and importing text tables with composite domain index created with FILTER BY and/or ORDER BY clauses are as follows:

• Regular exp and imp will not support exporting and importing of composite domain index. Doing so will lead to the following error: EXP-00113: Feature Composite Domain Index is unsupported.

• To export a text table with composite domain index, you must use Data Pump Export and Import utilities (invoked with the expdp and impdp commands, respectively), or DBMS_DATAPUMP PL/SQL package.

Limitations of using ALTER INDEX and ALTER TABLE with FILTER BY and ORDER BY columns of the composite domain index, which are imposed by Extensible Indexing Framework in Oracle Database:

(These limitations are imposed by Extensible Indexing Framework in Oracle Database.)

• Using ALTER INDEX to add or drop FILTER BY and ORDER BY columns is currently not supported. You must re-create the index to add or drop FILTER BY or ORDER BY columns.

• To use ALTER TABLE MODIFY COLUMN to modify the datatype of a column that has the composite domain index built on it, you must first drop the composite domain index before modifying the column.

• To use ALTER TABLE DROP COLUMN to drop a column that is part of the composite domain index, you must first drop the composite domain index before dropping the index column.

The following limitations apply to FILTER BY and ORDER BY when used with PL/SQL packages:

• Mapping FILTER BY columns to sections is optional. If section mapping does not exist for a FILTER BY column, then it is mapped to an SDATA section by default. The section name assumes the name of the FILTER BY column.

• If a section group is not specified during the CREATE INDEX clause of a composite domain index, then system default section group settings are used. An SDATA section is created for each of the FILTER BY and ORDER BY columns.

  Note:

  Because a section name does not allow certain special characters and is case-insensitive, if the column name is case-sensitive or contains special characters, then an error will be raised. To work around this problem, you must map the column to an MDATA or SDATA section before creating the index. See CTX_DDL.ADD_MDATA_COLUMN or CTX_DDL.ADD_SDATA_COLUMN.

• An error is raised if a column that is mapped to an MDATA section also appears in the ORDER BY column clause.

• Column section names are unique to their section group. That is, you cannot have an MDATA column section named FOO if you already have an MDATA column section named FOO. Nor can you have a field section named FOO if you already have an SDATA column section named FOO. This is true whether it is implicitly created (by CREATE INDEX for FILTER BY or ORDER BY clauses) or explicitly created (by CTX_DDL.ADD_SDATA_COLUMN).

• One section name can be mapped to only one FILTER BY column, and vice versa. Mapping a section to more than one column, or mapping a column to more than one section is not allowed.

• Column sections can be added to any type of section group, including the NULL section group.

• If a section group with sections added by the CTX_DDL.ADD_MDATA_COLUMN or CTX_DDL.ADD_SDATA_COLUMN packages is specified for a CREATE INDEX statement without a FILTER BY clause, then the mapped column sections will be ignored. However, the index will still get created without those column sections. The same is true for a FILTER BY clause that does not contain mapped columns in the specified section group.

LOCAL [PARTITION [partition] [PARAMETERS('paramstring')]

Specifies a local partitioned context index on a partitioned table. The partitioned table must be partitioned by range. Hash, composite, and list partitions are not supported.

You can specify the list of index partition names with partition_name. If you do not specify a partition name, then the system assigns one. The order of the index partition list must correspond to the table partition order.

The PARAMETERS clause associated with each partition specifies the parameters string specific to that partition. You can only specify sync (manual|every |on commit), memory and storage for each index partition.

The PARAMETERS clause also supports the POPULATE and NOPOPULATE arguments. See "POPULATE | NOPOPULATE".

Query the views CTX_INDEX_PARTITIONS or CTX_USER_INDEX_PARTITIONS to find out index partition information, such as index partition name, and index partition status.

See Also:

"Creating a Local Partitioned Index"

Query Performance Limitation with Partitioned Index

For optimal performance when querying a partitioned index with an ORDER BY SCORE clause, query the partition. If you query the entire table and use an ORDER BY SCORE clause, the query might not perform optimally unless you include a range predicate that can limit the query to the fewest number of partitions, which is optimally a single partition.

PARALLEL n

Optionally specifies the parallel degree for parallel indexing. The actual degree of parallelism might be smaller depending on your resources. You can use this parameter on nonpartitioned tables. However, creating a nonpartitioned index in parallel does not turn on parallel query processing. Parallel indexing is supported for creating a local partitioned index.

The indexing memory size specified in the parameter clause applies to each parallel slave. For example, if indexing memory size is specified in the parameter clause as 500M and parallel degree is specified as 2, then you must ensure that there is at least 1GB of memory available for indexing.

See Also:

• "Parallel Indexing"

• "Creating a Local Partitioned Index in Parallel"

• The "Performance Tuning" chapter in Oracle Text Application Developer's Guide

Performance

Parallel indexing can speed up indexing when you have large amounts of data to index and when your operating system supports multiple CPUs.

Limitations

Parallel indexing is supported only for the CONTEXT index type.

UNUSABLE

Creates an unusable index. This creates index metadata only and exits immediately.

You might create an unusable index when you need to create a local partitioned index in parallel.

See Also:

"Creating a Local Partitioned Index in Parallel"

PARAMETERS(paramstring)

Optionally specify indexing parameters in paramstring. You can specify preferences owned by another user using the user.preference notation.

The syntax for paramstring is as follows:

paramstring = 

'[DATASTORE datastore_pref] 
 [FILTER filter_pref] 
 [CHARSET COLUMN charset_column_name]  
 [FORMAT COLUMN format_column_name]
 [SAVE_COPY COLUMN save_copy_column_name] 

 [LEXER lexer_pref]
 [LANGUAGE COLUMN language_column_name] 

 [WORDLIST wordlist_pref] 
 [STORAGE storage_pref] 
 [STOPLIST stoplist] 
 [SECTION GROUP section_group]
 [MEMORY memsize]
 [POPULATE | NOPOPULATE]
 [SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)]
 [TRANSACTIONAL]'

Create datastore, filter, lexer, wordlist, and storage preferences with CTX_DDL.CREATE_PREFERENCE and then specify them in the paramstring.

Note:

When you specify no paramstring, Oracle Text uses the system defaults.

For more information about these defaults, see "Default Index Parameters".

DATASTORE datastore_pref

Specifies the name of your datastore preference. Use the datastore preference to specify where your text is stored.See "Datastore Types".

FILTER filter_pref

Specifies the name of your filter preference. Use the filter preference to specify how to filter formatted documents to plain text or HTML. See "Filter Types".

CHARSET COLUMN charset_column_name

Specifies the name of the character set column. This column must be in the same table as the text column, and it must be of type CHAR, VARCHAR, or VARCHAR2. Use this column to specify the document character set for conversion to the database character set. The value is case-insensitive. You must specify a globalization support character set string, such as JA16EUC.

When the document is plain text or HTML, the AUTO_FILTER and CHARSET filters use this column to convert the document character set to the database character set for indexing.

Use this column when you have plain text or HTML documents with different character sets or in a character set different from the database character set.

Setting NLS_LENGTH_SEMANTICS parameter to CHAR is not supported at the database level. This parameter is supported for the following columns:

• The CHARSET COLUMN, for example:

  VARCHAR2 <size> CHAR
  CHAR <size> CHAR
  

• An index created on a VARCHAR2 and CHAR column

• VARCHAR2 and CHAR columns for FILTER BY and ORDER BY clauses of CREATE INDEX

• FORMAT COLUMN

Note:

• Documents are not marked for re-indexing when only the character set column changes. The indexed column must be updated to flag the re-index.

• The NLS_LENGTH_SEMANTICS = CHAR parameter is supported at the column level only, and is not supported at the database level, as described in this section.

FORMAT COLUMN format_column_name

Specifies the name of the format column. The format column must be in the same table as the text column and it must be CHAR, VARCHAR, or VARCHAR2 type.

FORMAT COLUMN determines how a document is filtered, or, in the case of the IGNORE value, if it is to be indexed.

AUTO_FILTER uses the format column when filtering documents. Use this column with heterogeneous document sets to optionally bypass filtering for plain text or HTML documents.

In the format column, you can specify one of the following options:

• TEXT

• BINARY

• IGNORE

The TEXT option indicates that the document is either plain text or HTML. When TEXT is specified, the document is not filtered, but may have the character set converted.

The BINARY option indicates that the document is a format supported by the AUTO_FILTER object other than plain text or HTML, for example PDF. BINARY is the default, if the format column entry cannot be mapped.

The IGNORE option indicates that the row is to be ignored during indexing. Use this value when you need to bypass rows that contain data incompatible with text indexing such as image data, or rows in languages that you do not want to process. The difference between documents with TEXT and IGNORE format column types is that the former are indexed but ignored by the filter, while the latter are not indexed at all. Thus, IGNORE can be used with any filter type.

Note:

Documents are not marked for re-indexing when only the format column changes. The indexed column must be updated to flag the re-index.

SAVE_COPY COLUMN save_copy_column_name

Specifies the name of the column that contains the preference of whether to save a copy of a document into the $D index table during a search operation.

You can specify one of the following three options in the SAVE_COPY column: PLAINTEXT, FILTERED, or NONE.

The PLAINTEXT option indicates that the document should be stored as a plain text in the $D index table. Specify this value when using the SNIPPET procedure.

The FILTERED option indicates that a filter preference should be applied on the text present in the document before storing it into the $D index table. Specify this value when using the MARKUP procedure or the HIGHLIGHT procedure.

The NONE option indicates that a copy of the document should not be saved in the $D index table. Specify this value for any of the following scenarios:

• when SNIPPET, MARKUP, or HIGHLIGHT procedure is not used.

• when the indexed column is either VARCHAR2 or CLOB.

LEXER lexer_pref

Specifies the name of your lexer or multilexer preference. Use the lexer preference to identify the language of your text and how text is tokenized for indexing. See "Lexer Types".

LANGUAGE COLUMN language_column_name

Specifies the name of the language column when using a multi-lexer preference. See "MULTI_LEXER".

This column must exist in the base table. It cannot be the same column as the indexed column. Only the first 30 bytes of the language column are examined for language identification.

Note:

Documents are not marked for re-indexing when only the language column changes. The indexed column must be updated to flag the re-index.

WORDLIST wordlist_pref

Specifies the name of your wordlist preference. Use the wordlist preference to enable features such as fuzzy, stemming, and prefix indexing for better wildcard searching. See "Wordlist Type".

STORAGE storage_pref

Specifies the name of your storage preference for the Text index. Use the storage preference to specify how the index tables are stored. See "Storage Types".

STOPLIST stoplist

Specifies the name of your stoplist. Use stoplist to identify words that are not to be indexed. See CTX_DDL.CREATE_STOPLIST.

SECTION GROUP section_group

Specifies the name of your section group. Use section groups to create searchable sections in structured documents. See CTX_DDL.CREATE_SECTION_GROUP.

MEMORY memsize

Specifies the amount of run-time memory to use for indexing. The syntax for memsize is as follows:

memsize = number[K|M|G]

K stands for kilobytes, M stands for megabytes, and G stands for gigabytes.

The value you specify for memsize must be between 1M and the value of MAX_INDEX_MEMORY in the CTX_PARAMETERS view. To specify a memory size larger than the MAX_INDEX_MEMORY, you must reset this parameter with CTX_ADM.SET_PARAMETER to be larger than or equal to memsize.

The default is the value specified for DEFAULT_INDEX_MEMORY in CTX_PARAMETERS.

The memsize parameter specifies the amount of memory Oracle Text uses for indexing before flushing the index to disk. Specifying a large amount memory improves indexing performance because there are fewer I/O operations and improves query performance and maintenance, because there is less fragmentation.

Specifying smaller amounts of memory increases disk I/O and index fragmentation, but might be useful when run-time memory is scarce.

POPULATE | NOPOPULATE

Specifies whether an index should be empty or populated. The default is POPULATE.

Note:

POPULATE | NOPOPULATE is the only option whose default value cannot be set with CTX_ADM.SET_PARAMETER.

Empty indexes are populated by updates or inserts to the base table. You might create an empty index when you need to create your index incrementally or to selectively index documents in the base table. You might also create an empty index when you require only theme and Gist output from a document set.

SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)

Specifies SYNC for automatic synchronization of the CONTEXT index when there are inserts, updates or deletes to the base table. You can specify one of the following SYNC methods:

Table 1-5 SYNC Types

SYNC Type	Description
MANUAL	Provides no automatic synchronization. This is the default. You must manually synchronize the index with CTX_DDL.SYNC_INDEX.
EVERY "interval-string"	Automatically synchronizes the index at a regular interval specified by the value of interval-string, which takes the same syntax as that for scheduler jobs. Automatic synchronization using EVERY requires that the index creator have CREATE JOB privileges. Ensure that interval-string is set to a long enough period that any previous sync jobs will have completed; otherwise, the sync job might hang. interval-string must be enclosed in double quotes, and any single quote within interval-string must be preceded by the escape character with another single quote. See "Enabling Automatic Index Synchronization" for an example of automatic sync syntax.
ON COMMIT	Synchronizes the index immediately after a commit transaction. The commit transaction does not return until the sync is complete. (Because the synchronization is performed as a separate transaction, there may be a period, usually small, when the data is committed but index changes are not.) The operation uses the memory specified with the memory parameter. Note that the sync operation has its own transaction context. If this operation fails, the data transaction is still committed. Index synchronization errors are logged in the CTX_USER_INDEX_ERRORS view. See "Viewing Index Errors". See "Enabling Automatic Index Synchronization" for an example of ON COMMIT syntax.

Each partition of a locally partitioned index can have its own type of sync (ON COMMIT, EVERY, or MANUAL). The type of sync specified in master parameter strings applies to all index partitions unless a partition specifies its own type.

With automatic (EVERY) synchronization, users can specify memory size and parallel synchronization. That syntax is:

... EVERY interval_string MEMORY mem_size PARALLEL paradegree ...

The ON COMMIT synchronizations can be run only serially and must use the same memory size that was specified at index creation.

See Also:

Oracle Database Administrator's Guide for information about job scheduling

TRANSACTIONAL

Specifies that documents can be searched immediately after they are inserted or updated. If a text index is created with TRANSACTIONAL enabled, then, in addition to processing the synchronized rowids already in the index, the CONTAINS operator will process unsynchronized rowids as well. Oracle Text does in-memory indexing of unsynchronized rowids and processes the query against the in-memory index.

TRANSACTIONAL is an index-level parameter and does not apply at the partition level.

You must still synchronize your text indexes from time to time (with CTX_DDL.SYNC_INDEX) to bring pending rowids into the index. Query performance degrades as the number of unsynchronized rowids increases. For that reason, Oracle recommends setting up your index to use automatic synchronization with the EVERY or ON COMMIT parameter. (See "SYNC (MANUAL | EVERY "interval-string" | ON COMMIT)".)

Transactional querying for indexes that have been created with the TRANSACTIONAL parameter can be turned on and off (for the duration of a user session) with the PL/SQL variable CTX_QUERY.disable_transactional_query. This is useful, for example, if you find that querying is slow due to the presence of too many pending rowids. Here is an example of setting this session variable:

exec ctx_query.disable_transactional_query := TRUE;

If the index uses AUTO_FILTER, queries involving unsynchronized rowids will require filtering of unsynchronized documents.

CREATE INDEX: CONTEXT Index Examples

The following sections give examples of creating a CONTEXT index.

Creating CONTEXT Index Using Default Preferences

The following example creates a CONTEXT index called myindex on the docs column in mytable. Default preferences are used.

CREATE INDEX myindex ON mytable(docs) INDEXTYPE IS ctxsys.context;

Creating CONTEXT Index with Custom Preferences

The following example creates a CONTEXT index called myindex on the docs column in mytable. The index is created with a custom lexer preference called my_lexer and a custom stoplist called my_stop.

This example also assumes that the preference and stoplist were previously created with CTX_DDL.CREATE_PREFERENCE for my_lexer, and CTX_DDL.CREATE_STOPLIST for my_stop. Default preferences are used for the unspecified preferences.

CREATE INDEX myindex ON mytable(docs) INDEXTYPE IS ctxsys.context 
  PARAMETERS('LEXER my_lexer STOPLIST my_stop');

Any user can use any preference. To specify preferences that exist in another user's schema, add the user name to the preference name. The following example assumes that the preferences my_lexer and my_stop exist in the schema that belongs to user kenny:

CREATE INDEX myindex ON mytable(docs) INDEXTYPE IS ctxsys.context 
  PARAMETERS('LEXER kenny.my_lexer STOPLIST kenny.my_stop');

Enabling Automatic Index Synchronization

You can create your index and specify that the index be synchronized at regular intervals for insertions, updates and deletions to the base table. To do so, create the index with the SYNC (EVERY "interval-string") parameter.

To use job scheduling, you must log in as a user who has DBA privileges and then grant CREATE JOB privileges.

The following example creates an index and schedules three synchronization jobs for three index partitions. The first partition uses ON COMMIT synchronization. The other two partitions are synchronized by jobs that are scheduled to be executed every Monday at 3 P.M.

CONNECT system/password
GRANT CREATE JOB TO dr_test

CREATE INDEX tdrmauto02x ON tdrmauto02(text)
   INDEXTYPE IS CTXSYS.CONTEXT local
   (PARTITION tdrm02x_i1 PARAMETERS('
   MEMORY 20m SYNC(ON COMMIT)'),
   PARTITION tdrm02x_i2,
   PARTITION tdrm02x_i3)  PARAMETERS('
   SYNC (EVERY "NEXT_DAY(TRUNC(SYSDATE), ''MONDAY'') + 15/24")
  ');

See Oracle Database Administrator's Guide for information about job scheduling syntax.

Creating CONTEXT Index with Multilexer Preference

The multilexer preference decides which lexer to use for each row based on a language column. This is a character column in the table that stores the language of the document in the text column. For example, create the table globaldoc to hold documents of different languages:

CREATE TABLE globaldoc (
   doc_id NUMBER PRIMARY KEY,
   lang VARCHAR2(10),
   text CLOB
);

Assume that global_lexer is a multilexer preference you created. To index the global_doc table, specify the multilexer preference and the name of the language column as follows:

CREATE INDEX globalx ON globaldoc(text) INDEXTYPE IS ctxsys.context PARAMETERS
('LEXER global_lexer LANGUAGE COLUMN lang');

Creating a Local Partitioned Index

The following example creates a text table that is partitioned into three, populates it, and then creates a partitioned index:

PROMPT create partitioned table and populate it

CREATE TABLE part_tab (a int, b varchar2(40)) PARTITION BY RANGE(a)

(partition p_tab1 values less than (10),
 partition p_tab2 values less than (20),
 partition p_tab3 values less than (30));

PROMPT create partitioned index
CREATE INDEX part_idx on part_tab(b) INDEXTYPE IS CTXSYS.CONTEXT

LOCAL (partition p_idx1, partition p_idx2, partition p_idx3);

Using FILTER BY and ORDER BY Clauses

The following example creates an index on table docs and orders the documents by author's publishing date.

First, create the table:

CREATE TABLE docs (
    docid    NUMBER, 
    pub_date DATE, 
    author   VARCHAR2(30), 
    category VARCHAR2(30), 
    document CLOB
);
 

Create the index with FILTER BY and ORDER BY clauses:

CREATE INDEX doc_idx on docs(document) indextype is ctxsys.context
  FILTER BY category, author
  ORDER BY pub_date desc, docid
  PARAMETERS ('memory 500M');

Parallel Indexing

Parallel indexing can improve index performance when you have multiple CPUs.

To create an index in parallel, use the PARALLEL clause with a parallel degree. This example uses a parallel degree of 3:

CREATE INDEX myindex ON mytab(pk) INDEXTYPE IS ctxsys.context PARALLEL 3;

Creating a Local Partitioned Index in Parallel

Creating a local partitioned index in parallel can improve performance when you have multiple CPUs. With partitioned tables, you can divide the work. You can create a local partitioned index in parallel in two ways:

• Use the PARALLEL clause with the LOCAL clause in the CREATE INDEX statement. In this case, the maximum parallel degree is limited to the number of partitions you have. See "Parallelism with CREATE INDEX".

• Create an unusable index first, then run the DBMS_PCLXUTIL.BUILD_PART_INDEX utility. This method can result in a higher degree of parallelism, especially if you have more CPUs than partitions. See "Parallelism with DBMS_PCLUTIL.BUILD_PART_INDEX".

If you attempt to create a local partitioned index in parallel, and the attempt fails, you may see the following error message:

ORA-29953: error in the execution of the ODCIIndexCreate routine for one or more
of the index partitions

To determine the specific reason why the index creation failed, query the CTX_USER_INDEX_ERRORS view.

Parallelism with CREATE INDEX

You can achieve local index parallelism by using the PARALLEL and LOCAL clauses in the CREATE INDEX statement. In this case, the maximum parallel degree is limited to the number of partitions that you have.

The following example creates a table with three partitions, populates them, and then creates the local indexes in parallel with a degree of 2:

create table part_tab3(id number primary key, text varchar2(100)) 
partition by range(id) 
(partition p1 values less than (1000), 
 partition p2 values less than (2000), 
 partition p3 values less than (3000)); 

begin 
  for i in 0..2999 
  loop 
      insert into part_tab3 values (i,'oracle'); 
  end loop; 
end; 
/ 

create index part_tab3x on part_tab3(text) 
indextype is ctxsys.context local (partition part_tabx1, 
                                   partition part_tabx2, 
                                   partition part_tabx3) 
parallel 2;                                                              

Parallelism with DBMS_PCLUTIL.BUILD_PART_INDEX

You can achieve local index parallelism by first creating an unusable CONTEXT index, and then running the DBMS_PCLUTIL.BUILD_PART_INDEX utility. This method can result in a higher degree of parallelism, especially when you have more CPUs than partitions.

In this example, the base table has three partitions. We create a local partitioned unusable index first, then run DBMS_PCLUTIL.BUILD_PART_INDEX, which builds the 3 partitions in parallel (referred to as inter-partition parallelism). Also, inside each partition, index creation proceeds in parallel (called intra-partition parallelism) with a parallel degree of 2. Therefore, the total parallel degree is 6 (3 times 2).

create table part_tab3(id number primary key, text varchar2(100)) 
partition by range(id) 
(partition p1 values less than (1000), 
 partition p2 values less than (2000), 
 partition p3 values less than (3000)); 

begin 
  for i in 0..2999 
  loop 
      insert into part_tab3 values (i,'oracle'); 
  end loop; 
end; 
/ 

create index part_tab3x on part_tab3(text) 
indextype is ctxsys.context local (partition part_tabx1, 
                                   partition part_tabx2, 
                                   partition part_tabx3) 
unusable; 

exec dbms_pclxutil.build_part_index(jobs_per_batch=>3,
  procs_per_job=>2,
  tab_name=>'PART_TAB3',
  idx_name=>'PART_TAB3X',
  force_opt=>TRUE); 

Viewing Index Errors

After a CREATE INDEX or ALTER INDEX operation, you can view index errors with Oracle Text views. To view errors on your indexes, query the CTX_USER_INDEX_ERRORS view. To view errors on all indexes as CTXSYS, query the CTX_INDEX_ERRORS view.

For example, to view the most recent errors on your indexes, enter the following statement:

SELECT err_timestamp, err_text FROM ctx_user_index_errors
ORDER BY err_timestamp DESC;

Deleting Index Errors

To clear the index error view, enter the following statement:

DELETE FROM ctx_user_index_errors;

Syntax for CTXCAT Index Type

Combines an index on a text column and one or more other columns. Query this index with the CATSEARCH operator in the WHERE clause of a SELECT statement. This type of index is optimized for mixed queries. This index is transactional, automatically updating itself with DML to the base table.

CREATE INDEX [schema.]index on [schema.]table(column) INDEXTYPE IS ctxsys.ctxcat 

[PARAMETERS

('[index set index_set]
[lexer lexer_pref]
[storage storage_pref] 
[stoplist stoplist] 
[section group sectiongroup_pref]
[wordlist wordlist_pref] 
[memory memsize]');

[schema.]table(column)

Specifies the name of the table and column to index.

The column that you specify when you create a CTXCAT index must be of type CHAR or VARCHAR2. No other types are supported for CTXCAT.

Attempting to create an index on a Virtual Private Database (VPD) protected table will fail unless one of the following options is true:

• The VPD policy is created such that it does not apply to INDEX statement type, which is the default

• The policy function returns a null predicate for the current user.

• The user (index owner) is SYS.

• The user has the EXEMPT ACCESS POLICY privilege.

Supported CTXCAT Preferences

index set index_set

Specifies the index set preference to create the CTXCAT index. Index set preferences name the columns that make up your subindexes. Any column that is named in an index set column list cannot have a NULL value in any row of the base table, or else you get an error.

Always ensure that your columns have non-null values before and after indexing.

See "Creating a CTXCAT Index".

Index Performance and Size Considerations

Although a CTXCAT index offers query performance benefits, creating this type of index has its costs. The time that it takes Oracle Text to create a CTXCAT index depends on the total size of the index.

The total size of a CTXCAT index is directly related to:

• Total text to be indexed

• Number of component indexes in the index set

• Number of columns in the base table that make up the component indexes

Having many component indexes in your index set also degrades DML performance because more indexes must be updated.

Because of these added costs in creating a CTXCAT index, you should carefully consider the query performance benefit that each component index gives your application before adding it to your index set.

Other CTXCAT Preferences

When you create an index of type CTXCAT, you can use the supported index preferences listed in Table 1-6 in the parameters string.

Unsupported Preferences and Parameters

When you create a CTXCAT index, you cannot specify datastore and filter preferences. For section group preferences, only the field section preference is supported. You also cannot specify language, format, or charset columns as with a CONTEXT index.

Creating a CTXCAT Index

This section gives a brief example for creating a CTXCAT index. For a more complete example, see Oracle Text Application Developer's Guide.

Consider a table called AUCTION with the following schema:

create table auction(

item_id number,
title varchar2(100),
category_id number,
price number,
bid_close date);

Assume that queries on the table involve a mandatory text query clause and optional structured conditions on price. Results must be sorted based on bid_close. This means that an index to support good response time for the structured and sorting criteria is required.

You can create a catalog index to support the different types of structured queries a user might enter. For structured queries, a CTXCAT index improves query performance over a context index.

To create the indexes, first, create the index set preference, next, optionally, add the storage preference, and, finally, add the required indexes to it:

begin

ctx_ddl.create_index_set('auction_iset');
ctx_ddl.add_index('auction_iset','bid_close');
ctx_ddl.add_index('auction_iset','price, bid_close');

end;

Optionally, create the storage preference:

begin
 ctx_ddl.create_preference('auction_st_pref', 'BASIC_STORAGE');
 ctx_ddl.set_attribute('auction_st_pref', 'I_TABLE_CLAUSE',
                       'tablespace TEXT storage (initial 5M)');
 ctx_ddl.set_attribute('auction_st_pref', 'I_ROWID_INDEX_CLAUSE',
                        'tablespace TEXT storage (initial 5M)');
 ctx_ddl.set_attribute('auction_st_pref', 'I_INDEX_CLAUSE',
                        'tablespace TEXT storage (initial 5M) compress 2');
end;
/ 

Then, create the CTXCAT index with the CREATE INDEX statement as follows:

create index auction_titlex on AUCTION(title) indextype is CTXSYS.CTXCAT
parameters ('index set auction_iset storage auction_st_pref');

Querying a CTXCAT Index

To query the title column for the word pokemon, enter regular and mixed queries as follows:

select * from AUCTION where CATSEARCH(title, 'pokemon',NULL)> 0;
select * from AUCTION where CATSEARCH(title, 'pokemon', 'price < 50 order by
bid_close desc')> 0;

Syntax for CTXRULE Index Type

The CTXRULE type is an index on a column containing a set of queries. Query this index with the MATCHES operator in the WHERE clause of a SELECT statement.

CREATE INDEX [schema.]index on [schema.]table(rule_col) INDEXTYPE IS 

ctxsys.ctxrule 
[PARAMETERS ('[lexer lexer_pref] [storage storage_pref]

[section group section_pref] [wordlist wordlist_pref]
[classifier classifier_pref]');

[PARALLEL n];

[schema.]table(column)

Specifies the name of the table and rule column to index. The rules can be query compatible strings, query template strings, or binary Support Vector Machine rules.

The column you specify when you create a CTXRULE index must be VARCHAR2, CLOB or BLOB. No other types are supported for the CTXRULE type.

Attempting to create an index on a Virtual Private Database (VPD) protected table will fail unless one of the following is true:

• The VPD policy does not have the INDEX statement type turned on (which is the default).

• The policy function returns a null predicate for the current user.

• The user (index owner) is SYS.

• The user has the EXEMPT ACCESS POLICY privilege.

lexer_pref

Specifies the lexer preference to be used for processing queries and later for the documents to be classified with the MATCHES function.

With both classifiers SVN_CLASSFIER and RULE_CLASSIFIER, you can use the BASIC_LEXER, CHINESE_LEXER, JAPANESE_LEXER, or KOREAN_MORPH_LEXER lexer. (See "Classifier Types" and "Lexer Types".)

For processing queries, these lexers support the following operators: ABOUT, STEM, AND, NEAR, NOT, OR, and WITHIN.

The thesaural operators (BT*, NT*, PT, RT, SYN, TR, TRSYS, TT, and so on) are supported. However, these operators are expanded using a snapshot of the thesaurus at index time, not when the MATCHES function is entered. This means that if you change your thesaurus after you index, you must re-index your query set.

storage_pref

Specify the storage preference for the index on the queries.Use the storage preference to specify how the index tables are stored. See "Storage Types".

section group

Specify the section group. This parameter does not affect the queries. It applies to sections in the documents to be classified. The following section groups are supported for the CTXRULE index type:

• BASIC_SECTION_GROUP

• HTML_SECTION_GROUP

• XML_SECTION_GROUP

• AUTO_SECTION_GROUP

See "Section Group Types".

CTXRULE does not support special sections. It also does not support NDATA sections.

wordlist_pref

Specifies the wordlist preferences. This is used to enable stemming operations on query terms. See Wordlist Type.

classifier_pref

Specifies the classifier preference. See "Classifier Types". You must use the same preference name you specify with CTX_CLS.TRAIN.

Example for Creating a CTXRULE Index

See Oracle Text Application Developer's Guide for a complete example of using the CTXRULE index type in a document routing application.

Related Topics

CTX_DDL.CREATE_PREFERENCE

CTX_DDL.CREATE_STOPLIST

CTX_DDL.CREATE_SECTION_GROUP

"ALTER INDEX"

"CATSEARCH"

Purpose

Use DROP INDEX to drop a specified Text index.

Syntax

DROP INDEX [schema.]index [force];

[force]

Optionally forces the index to be dropped. Use the force option when Oracle Text cannot determine the state of the index, such as when an indexing operation fails.

Oracle recommends against using this option by default. Use it only when a regular call to DROP INDEX fails.

Example

The following example drops an index named doc_index in the current user's database schema:

DROP INDEX doc_index;

Related Topics

"ALTER INDEX"

"CREATE INDEX"

Limitation

If the optimizer chooses to use the functional query invocation with a MATCHES query, your query will fail.

Syntax

MATCHES(

[schema.]column,
document VARCHAR2 or CLOB
[,label INTEGER])

RETURN NUMBER;

column

Specifies the column containing the indexed query set.

document

Specifies the document to be classified. The document can be plain text, HTML, or XML. Binary formats are not supported.

label

Optionally specifies the label that identifies the score generated by the MATCHES operator. Use this label with MATCH_SCORE.

Matches Example

The following example creates a table querytable, and populates it with classification names and associated rules. It then creates a CTXRULE index.

The example enters the MATCHES query with a document string to be classified. The SELECT statement returns all rows (queries) that are satisfied by the document:

create table querytable (classification varchar2(64), text varchar2(4000));
insert into querytable values ('common names', 'smith OR jones OR brown');
insert into querytable values ('countries', 'United States OR Great Britain OR
France');
insert into querytable values ('Oracle DB', 'oracle NEAR database');

create index query_rule on querytable(text) indextype is ctxsys.ctxrule;

SELECT classification FROM querytable WHERE MATCHES(text, 'Smith is a common name
in the United States') > 0;


CLASSIFICATION
----------------------------------------------------------------
common names
countries

Related Topics

"MATCH_SCORE"

"Syntax for CTXRULE Index Type"

CTX_CLS.TRAIN

Oracle Text Application Developer's Guide contains extended examples of simple and supervised classification, which make use of the MATCHES operator.

Syntax

MATCH_SCORE(label NUMBER)

label

Specifies a number to identify the score produced by the query. Use this number to identify the MATCHES clause that returns this score.

Example

To get the matching score, use:

select cat_id, match_score(1) from training_result where matches(profile,
text,1)>0;

Related Topics

"MATCHES"

Syntax

SCORE(label NUMBER)

label

Specifies a number to identify the score produced by the query. Use this number to identify the CONTAINS clause that returns this score.

Example

Single CONTAINS

When the SCORE operator is called (for example, in a SELECT clause), the CONTAINS clause must reference the score label value as in the following example:

SELECT SCORE(1), title from newsindex 
           WHERE CONTAINS(text, 'oracle', 1) > 0 ORDER BY SCORE(1) DESC;

Multiple CONTAINS

Assume that a news database stores and indexes the title and body of news articles separately. The following query returns all the documents that include the words Oracle in their title and java in their body. The articles are sorted by the scores for the first CONTAINS (Oracle) and then by the scores for the second CONTAINS (java).

SELECT title, body, SCORE(10), SCORE(20)

FROM news
WHERE CONTAINS (news.title, 'Oracle', 10) > 0 OR

CONTAINS (news.body, 'java', 20) > 0 
ORDER BY SCORE(10), SCORE(20);

Related Topics

"CONTAINS"

Appendix F, " The Oracle Text Scoring Algorithm"