XMLQUERY scalar function
The XMLQUERY function returns an XML value from the evaluation of an XQuery expression possibly using specified input arguments as XQuery variables.
The schema is SYSIBM. The function name cannot be specified as a qualified name.
- Specifies an SQL character string constant that is interpreted as an XQuery expression using supported XQuery language syntax. The constant string is converted to UTF-8 before being parsed as an XQuery statement. The XQuery expression executes using an optional set of input XML values, and returns an output sequence that is also returned as the value of the XMLQUERY expression. The value for xquery-expression-constant must not be an empty string or a string of blank characters (SQLSTATE 10505).
- Specifies input values and the manner in which these values are
passed to the XQuery expression specified by xquery-expression-constant.
By default, every unique column name that is in the scope where the
function is invoked is implicitly passed to the XQuery expression
using the name of the column as the variable name. If an identifier in
a specified xquery-argument matches an in-scope column name, then
the explicit xquery-argument is passed to the XQuery expression overriding
that implicit column.
- BY REF
- Specifies that the default passing mechanism is by reference
for any xquery-variable-expression of data
type XML and for the returned value. When XML values are passed
by reference, the XQuery evaluation uses the input node trees, if
any, directly from the specified input expressions, preserving all
properties, including the original node identities and document order.
If two arguments pass the same XML value, node identity comparisons
and document ordering comparisons involving some nodes contained between
the two input arguments might refer to nodes within the same XML node
This clause has no impact on how non-XML values are passed. The non-XML values create a new copy of the value during the cast to XML.
an argument that is to be passed to the XQuery expression specified by
xquery-expression-constant. An argument specifies a value and the manner in which
that value is to be passed. xquery-argument specifies both a value and the manner
in which that value is to be passed. The method through which an argument, in the PASSING clause, is
used in the XQuery expression depends on whether the argument is specified as
xquery-context-item-expression or xquery-variable-expression.
xquery-argument includes an SQL expression that is evaluated before it passes the
result to the XQuery expression.
- If the resulting value is of type XML, it becomes an input-xml-value. A null XML value is converted to an XML empty sequence.
- If the resulting value is not of type XML, it must be castable to the XML data type. A null value is converted to an XML empty sequence. The converted value becomes an input-xml-value.
- xquery-context-item-expression specifies the initial context item in the XQuery expression that is specified by xquery-expression-constant. The value of the initial context item is the result of xquery-context-item-expression to XML. xquery-context-item-expression must not be specified more than one time. xquery-context-item-expression must not be a sequence of more than one item.
- If input-xml-value is an empty XML string, the XQuery expression is evaluated with the initial context item set to an empty XML string. If the value of input-xml-value is null, the function returns a null value. If the xquery-context-item-expression is not specified or is an empty sequence, the initial context item in the XQuery expression is undefined and the XQuery expression must not reference the initial context item.
- An XQuery variable is not created for the context item expression.
- Specifies an SQL expression whose value is available to the XQuery expression specified by xquery-expression-constant during execution. The expression cannot contain a sequence reference (SQLSTATE 428F9) or an OLAP function (SQLSTATE 42903). The data type of the expression cannot be DECFLOAT.
- AS identifier
- Specifies that the value generated by xquery-variable-expression will be passed to xquery-expression-constant as an XQuery variable. The variable name will be identifier. The leading dollar sign ($) that precedes variable names in the XQuery language is not included in identifier. The identifier must be a valid XQuery variable name and is restricted to an XML NCName (SQLSTATE 42634). The identifier must not be greater than 128 bytes in length. Two arguments within the same PASSING clause cannot use the same identifier (SQLSTATE 42711).
- BY REF
- Indicates that an XML input value is to be passed by reference. When XML values are passed by reference, the XQuery evaluation uses the input node trees, if any, directly from the specified input expressions, preserving all properties, including the original node identities and document order. If two arguments pass the same XML value, node identity comparisons and document ordering comparisons involving some nodes contained between the two input arguments might refer to nodes within the same XML node tree. If BY REF is not specified following an xquery-variable-expression, XML arguments are passed by way of the default passing mechanism that is provided through the syntax that follows the PASSING keyword. This option cannot be specified for non-XML values. When a non-XML value is passed, the value is converted to XML; this process creates a copy.
- RETURNING SEQUENCE
- Indicates that the XMLQUERY expression returns a sequence.
- BY REF
- Indicates that the result of the XQuery expression is returned by reference. If this value contains nodes, any expression using the return value of the XQuery expression will receive node references directly, preserving all node properties, including the original node identities and document order. Referenced nodes will remain connected within their node trees. If the BY REF clause is not specified and the PASSING is specified, the default passing mechanism is used. If BY REF is not specified and PASSING is not specified, the default returning mechanism is BY REF.
- EMPTY ON EMPTY
- Specifies that an empty sequence result from processing the XQuery expression is returned as an empty sequence.
The data type of the result is XML; it cannot be null.
If the evaluation of the XQuery expression results in an error, then the XMLQUERY function returns the XQuery error (SQLSTATE class '10').
- XMLQUERY usage restrictions: The XMLQUERY function cannot
- Part of the ON clause that is associated with a JOIN operator or a MERGE statement (SQLSTATE 42972)
- Part of the GENERATE KEY USING or RANGE THROUGH clause in the CREATE INDEX EXTENSION statement (SQLSTATE 428E3)
- Part of the FILTER USING clause in the CREATE FUNCTION (External Scalar) statement, or the FILTER USING clause in the CREATE INDEX EXTENSION statement (SQLSTATE 428E4)
- Part of a check constraint or a column generation expression (SQLSTATE 42621)
- Part of a group-by-clause (SQLSTATE 42822)
- Part of an argument for a column-function (SQLSTATE 42607)
- XMLQUERY as a subquery: An XMLQUERY expression that acts as a subquery can be restricted by statements that restrict subqueries.