XMLTABLE

Syntax

XMLnamespaces_clause::=

XMLTABLE_options::=

XML_passing_clause::=

XML_table_column::=

Purpose

XMLTable maps the result of an XQuery evaluation into relational rows and columns. You can query the result returned by the function as a virtual relational table using SQL.

• The XMLNAMESPACES clause contains a set of XML namespace declarations. These declarations are referenced by the XQuery expression (the evaluated XQuery_string), which computes the row, and by the XPath expression in the PATH clause of XML_table_column, which computes the columns for the entire XMLTable function. If you want to use qualified names in the PATH expressions of the COLUMNS clause, then you need to specify the XMLNAMESPACES clause.

• XQuery_string is a literal string. It is a complete XQuery expression and can include prolog declarations. The value of XQuery_string serves as input to the XMLTable function; it is this XQuery result that is decomposed and stored as relational data.

• The expr in the XML_passing_clause is an expression returning an XMLType or an instance of a SQL scalar data type that is used as the context for evaluating the XQuery expression. You can specify only one expr in the PASSING clause without an identifier. The result of evaluating each expr is bound to the corresponding identifier in the XQuery_string. If any expr that is not followed by an AS clause, then the result of evaluating that expression is used as the context item for evaluating the XQuery_string. This clause supports only passing by value, not passing by reference. Therefore, the BY VALUE keywords are optional and are provided for semantic clarity.

• The optional RETURNING SEQUENCE BY REF clause causes the result of the XQuery evaluation to be returned by reference. This allows you to refer to any part of the source data in the XML_table_column clause.

  If you omit this clause, then the result of the XQuery evaluation is returned by value. That is, a copy of the targeted nodes is returned instead of a reference to the actual nodes. In this case, you cannot refer to any data that is not in the returned copy in the XML_table_column clause. In particular, you cannot refer to data that precedes the targeted nodes in the source data.

• The optional COLUMNS clause defines the columns of the virtual table to be created by XMLTable.

  • If you omit the COLUMNS clause, then XMLTable returns a row with a single XMLType pseudocolumn named COLUMN_VALUE.

  • FOR ORDINALITY specifies that column is to be a column of generated row numbers. There must be at most one FOR ORDINALITY clause. It is created as a NUMBER column.

  • For each resulting column except the FOR ORDINALITY column, you must specify the column data type, which can be XMLType or any other data type.

    If the column data type is XMLType, then specify the XMLTYPE clause. If you specify the optional (SEQUENCE) BY REF clause, then a reference to the source data targeted by the PATH expression is returned as the column content. Otherwise, column contains a copy of that targeted data.

    Returning the XMLType data by reference lets you specify other columns whose paths target nodes in the source data that are outside those targeted by the PATH expression for column.

    If the column data type is any other data type, then specify datatype.

  • The optional PATH clause specifies that the portion of the XQuery result that is addressed by XQuery expression string is to be used as the column content.

    If you omit PATH, then the XQuery expression column is assumed. For example:

    XMLTable(... COLUMNS xyz)
    

    is equivalent to

    XMLTable(... COLUMNS xyz PATH 'XYZ')
    

    You can use different PATH clauses to split the XQuery result into different virtual-table columns.

  • The optional DEFAULT clause specifies the value to use when the PATH expression results in an empty sequence. Its expr is an XQuery expression that is evaluated to produce the default value.

Examples

The following example converts the result of applying the XQuery '/Warehouse' to each value in the warehouse_spec column of the warehouses table into a virtual relational table with columns Water and Rail:

SELECT warehouse_name warehouse,
   warehouse2."Water", warehouse2."Rail"
   FROM warehouses,
   XMLTABLE('/Warehouse'
      PASSING warehouses.warehouse_spec
      COLUMNS 
         "Water" varchar2(6) PATH 'WaterAccess',
         "Rail" varchar2(6) PATH 'RailAccess') 
      warehouse2;

WAREHOUSE                           Water  Rail
----------------------------------- ------ ------
Southlake, Texas                    Y      N
San Francisco                       Y      N
New Jersey                          N      N
Seattle, Washington                 N      Y