Oracle® Database Gateway for SQL Server User's Guide, 11g Release 2 (11.2) Part Number E12069-01 |
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PDF · Mobi · ePub |
The Oracle Database Gateway for SQL Server translates a query that refers to an Oracle database data dictionary table into a query that retrieves the data from SQL Server system tables. You perform queries on data dictionary tables over the database link in the same way you query data dictionary tables in the Oracle database. The gateway data dictionary is similar to the Oracle database data dictionary in appearance and use.
This appendix contains the following sections:
The following paragraphs describe the Oracle Database Gateway for SQL Server data dictionary support.
SQL Server data dictionary information is stored in the SQL Server database as SQL Server system tables. All SQL Server system tables have names prefixed with "sys
". The SQL Server system tables define the structure of a database. When you change data definitions, SQL Server reads and modifies the SQL Server system tables to add information about the user tables.
Accessing a gateway data dictionary table or view is identical to accessing a data dictionary in an Oracle database. You issue a SQL SELECT
statement specifying a database link. The Oracle database data dictionary view and column names are used to access the gateway data dictionary in an Oracle database. Synonyms of supported views are also acceptable. For example, the following statement queries the data dictionary table ALL_CATALOG
to retrieve all table names in the SQL Server database:
SQL> SELECT * FROM "ALL_CATALOG"@MSQL;
When a data dictionary access query is issued, the gateway:
Maps the requested table, view, or synonym to one or more SQL Server system table names. The gateway translates all data dictionary column names to their corresponding SQL Server column names within the query. If the mapping involves one SQL Server system table, the gateway translates the requested table name to its corresponding SQL Server system table name within the query. If the mapping involves multiple SQL Server system tables, the gateway constructs a join in the query using the translated SQL Server system table names.
Sends the translated query to SQL Server.
Might convert the retrieved SQL Server data to give it the appearance of the Oracle database data dictionary table.
Passes the data dictionary information from the translated SQL Server system table to the Oracle database.
Note:
The values returned when querying the gateway data dictionary might not be the same as the ones returned by the Oracle SQL*PlusDESCRIBE
command.Queries issued directly to individual SQL Server system tables are allowed but they return different results because the SQL Server system table column names differ from those of the data dictionary view. Also, certain columns in an SQL Server system table cannot be used in data dictionary processing.
The gateway supports the following views and tables:
Supported Views and Table | Supported Views and Table |
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ALL_CATALOG |
ALL_COL_COMMENTS |
ALL_CONS_COLUMNS |
ALL_CONSTRAINTS |
ALL_IND_COLUMNS |
ALL_INDEXES |
ALL_OBJECTS |
ALL_TAB_COLUMNS |
ALL_TAB_COMMENTS |
ALL_TABLES |
ALL_USERS |
ALL_VIEWS |
DBA_CATALOG |
DBA_COL_COMMENTS |
DBA_OBJECTS |
DBA_TAB_COLUMNS |
DBA_TAB_COMMENTS |
DBA_TABLES |
DICT_COLUMNS |
DICTIONARY |
DUAL |
TABLE_PRIVILEGES |
USER_CATALOG |
USER_COL_COMMENTS |
USER_CONS_COLUMNS |
USER_CONSTRAINTS |
USER_IND_COLUMNS |
USER_INDEXES |
USER_OBJECTS |
USER_TAB_COLUMNS |
USER_TAB_COMMENTS |
USER_TABLES |
USER_USERS |
USER_VIEWS |
No other Oracle database data dictionary tables or views are supported. If you use a view not on the list, you will receive the Oracle database error code for no more rows available.
Queries through the gateway of any data dictionary table or view beginning with ALL_ can return rows from the SQL Server database even when access privileges for those SQL Server objects have not been granted. When querying an Oracle database with the Oracle data dictionary, rows are returned only for those objects you are permitted to access.
The tables in this section list Oracle data dictionary view names and the equivalent SQL Server system tables used. A plus sign (+) indicates that a join operation is involved.
Table C-1 Oracle Data Dictionary View Names and SQL Server Equivalents
View Name | SQL Server System Table Name |
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There is a minor difference between the gateway data dictionary and a typical Oracle database data dictionary. The Oracle database columns that are missing in an SQL Server system table are filled with zeros, spaces, null values, not-applicable values (N.A.), or default values, depending on the column type.
The gateway data dictionary tables and views provide the following information:
Name, data type, and width of each column
The contents of columns with fixed values
They are described here with information retrieved by an Oracle SQL*Plus DESCRIBE
command. The values in the Null?
column might differ from the Oracle database data dictionary tables and views. Any default value is shown to the right of an item, but this is not information returned by DESCRIBE
.
Note:
The column width of some columns in the translated data dictionary tables would be different when the gateway connects to a SQL Server Version 7.0 database.Name | Type | Value |
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