XMLGROUP

The XMLGROUP function returns an XML value that is a well-formed XML document.

Notes:

¹ The same clause must not be specified more than once.

expression

The content of each XML element is specified by an expression. The data type of expression must not be ROWID or DATALINK or a distinct type that is based on ROWID or DATALINK. The expression can be any SQL expression. If the expression is not a simple column reference, an element name must be specified. When AS ATTRIBUTES is specified, the data type of expression must not be XML or a distinct type that is based on XML.

AS qname-identifier

Specifies the XML element name or attribute name as an SQL identifier. The qname-identifier must be of the form of an XML qualified name, or QName. See the W3C XML namespace specifications for more details on valid names. If the name is qualified, the namespace prefix must be declared within the scope. If qname-identifier is not specified, expression must be a column name. The element name or attribute name is created from the column name using the fully escaped mapping from a column name to a QName.

ORDER BY

Specifies the order of the rows from the same grouping set that are processed in the aggregation. If the ORDER BY clause is not specified, or if the ORDER BY clause cannot differentiate the order of the sort key value, the rows in the same grouping set are arbitrarily ordered.

sort-key-expression: Specifies a sort key value that is either a column name or an expression. The data type of the column or expression must not be a DATALINK or XML value.; The ordering is based on the values of the sort keys, which might or might not be used in XML-expression.

OPTION

Specifies additional options for constructing the XML value. If no OPTION clause is specified, the default behavior applies.

ROW row-name: Specifies the name of the element to which each row is mapped. If this option is not specified, the default element name is "row".
ROOT root-name: Specifies the name of the root element. If this option is not specified, the default root element name is "rowset".
AS ATTRIBUTES: Specifies that each expression is mapped to an attribute value with column name or qname-identifier serving as the attribute name.

If a collating sequence other than *HEX is in effect when the statement that contains the XMLGROUP function is executed and the sort-key-expressions are SBCS data, mixed data, or Unicode data, then the result is obtained by comparing weighted values. The weighted values are derived by applying the collating sequence to the sort-key-expressions.

The result of the function is XML. The result can be null. If the set of values is empty, the result is the null value. Otherwise, the result is an XML sequence containing an item for each value in the set.

Notes

The default behavior defines a simple mapping between a result set and an XML value Some additional notes about function behavior apply:

By default, each row is transformed into an XML element named "row" and each expression is transformed into a nested element with the column name or qname-identifier as the element name.
The null handling behavior is NULL ON NULL. A null value for an expression maps to the absence of the subelement. If all expression values are null, no row element is generated. If no row elements are generated, the function returns the null value.
The binary encoding scheme for binary and FOR BIT DATA data types is base64Binary encoding.
The order of the row subelements in the root element will be the same as the order in which the rows are returned in the query result set.

Examples

Note: XMLGROUP does not insert blank spaces or new line characters in the output. All example output has been formatted to enhance readability.

Assume the following table T1 with columns C1 and C2:

 C1    C2
----  ----
  1     2
  -     2
  1     -
  -     -

The following example shows an XMLGROUP query and output fragment with default behavior, using a single top-level element to represent the table:
```
SELECT XMLGROUP(C1, C2) FROM T1   
```
Returns the following value for the single result row:
```
<rowset>
<row><C1>1</C1><C2>2</C2></row>
<row><C2>2</C2></row>
<row><C1>1</C1></row>
</rowset>
```
The following example shows an XMLGROUP query and output fragment with attribute centric mapping. Instead of appearing as nested elements as in the previous example, the data is mapped to element attributes:
```
SELECT XMLGROUP(C1, C2 OPTION AS ATTRIBUTES) FROM T1   
```
Returns the following value for the single result row:
```
<rowset>
<row C1="1" C2="2"/>
<row C2="2"/>
<row C1="1"/>
</rowset>
```
The following example shows an XMLGROUP query and output fragment with the default <rowset> root element replaced by <document> and the default <row> element replaced by <entry>. Columns C1 and C2 are returned as <column1> and <column2> elements, and the return set is ordered by column C1:
```
SELECT XMLGROUP(C1 AS "column1", C2 AS "column2"
                ORDER BY C1 OPTION ROW "entry" ROOT "document")
       FROM T1
```
Returns the following value for the single result row:
```
<document>
<entry> <column1>1</column1><column2>2</column2></entry>
<entry> <column1>1</column1></entry>
<entry> <column2>2</column2></entry>
</document>
```