XMLAGG is a function in PL/SQL that is used to aggregate XML elements into a single XML element. This function is particularly useful when you want to concatenate multiple XML elements into a single XML element, often as part of a larger SQL query or PL/SQL block.
The syntax for XMLAGG is as follows:
XMLAGG(XMLType_instance_expression [ORDER BY_clause])
XMLType_instance_expression: This is the XML element or elements that you want to aggregate. It can be a column, an expression, or a literal that evaluates to an XMLType.
ORDER BY_clause: Optional. If specified, it determines the order in which the XML elements are concatenated.
Here’s a simple example to illustrate the usage of XMLAGG. Suppose you have a table called employees with columns employee_id and employee_name, and you want to aggregate the employee names into a single XML element:
SELECT XMLAGG(XMLELEMENT("employee", employee_name) ORDER BY employee_id) AS aggregated_xml FROM employees;
In this example, XMLELEMENT(“employee”, employee_name) creates an XML element for each employee name, and XMLAGG aggregates these elements into a single XML element. The ORDER BY clause is optional but can be used to specify the order in which the employee names are concatenated.
The result might look something like this:
<aggregated_xml> <employee>John Doe</employee> <employee>Jane Smith</employee> <!-- ... other employee names ... --> </aggregated_xml>
You can use the result in further processing or store it in an XMLType column.
Keep in mind that XMLAGG is just one of many XML functions available in PL/SQL for working with XML data. Other functions, such as XMLPARSE and XMLQUERY, can be used to parse and query XML data within your PL/SQL code.