XMLTABLE

Syntax

XMLnamespaces_clause::=

XMLTABLE_options::=

XML_passing_clause::=

Description of the illustration xml_passing_clause.gif

XML_table_column::=

Description of the illustration xml_table_column.gif

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 complete XQuery expression and can include prolog declarations.

• 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.

• 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.

  • The datatype is required unless XMLTable is used with XML schema-based storage of XMLType, datatype. In this case, if you omit datatype, Oracle XML DB infers the data type from the XML schema. If the database is unable to determine the proper type for a node, then a default type of VARCHAR2(4000) is used.

  • 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.

  • 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.

  • 
    

    See Also:

    Oracle XML DB Developer‘s Guide for more information on the XMLTable function, including additional examples, and on XQuery in general

  • 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 ‘/Warehouse/WaterAccess‘,
             "Rail" varchar2(6) PATH ‘/Warehouse/RailAccess‘) 
          warehouse2;
    
    WAREHOUSE                           Water  Rail
    ----------------------------------- ------ ------
    Southlake, Texas                    Y      N
    San Francisco                       Y      N
    New Jersey                          N      N
    Seattle, Washington                 N      Y
    

    
    

XMLTABLE

原文：http://blog.csdn.net/cai_xingyun/article/details/18225077