SQL XMLELEMENT

What is SQL XMLELEMENT?

XMLELEMENT builds an XML element node from a tag name, optional attributes, and child content.

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Compatible dialects for SQL XMLELEMENT: PostgreSQL, Oracle Database, IBM Db2, SQL Server (via FOR XML, not XMLELEMENT), H2, Firebird. Not supported in MySQL or SQLite.

SQL XMLELEMENT Full Explanation

XMLELEMENT is an SQL/XML constructor that produces a well-formed XML element. You supply the element name, optional XMLATTRIBUTES(), and one or more content expressions. The function returns a value of the XML data type (or VARCHAR/NCLOB in some systems) that can be further queried or stored. Because it is evaluated per row, each invocation can generate different XML based on column values. XMLELEMENT is part of the SQL:2003 SQL/XML standard and is supported by engines that implement native XML types (PostgreSQL, Oracle, DB2, etc.). The element name must be a valid XML local name. Content expressions are concatenated in the order provided and automatically escaped. Null content is skipped unless the NULL ON NULL clause is used (PostgreSQL).

SQL XMLELEMENT Syntax

XMLELEMENT(
  NAME element_name
  [, XMLATTRIBUTES ( attr_value AS attr_name [, ... ] )]
  [, content_expr [, ... ]]
);

SQL XMLELEMENT Parameters

element_name STRING - Tag name of the element.
XMLATTRIBUTES clause - Optional list that maps SQL expressions to attribute names.
content_expr ANY - One or more expressions that become the element’s children (text nodes or nested XML).

Example Queries Using SQL XMLELEMENT

-- 1. Simple element
SELECT XMLELEMENT(NAME emp, 'John Doe');

-- 2. Element with dynamic name and attribute
SELECT XMLELEMENT(NAME employee,
       XMLATTRIBUTES(e.id AS emp_id),
       e.first_name || ' ' || e.last_name) AS emp_xml
FROM employees e
LIMIT 1;

-- 3. Nested elements
SELECT XMLELEMENT(NAME order,
         XMLATTRIBUTES(o.order_id AS id),
         XMLELEMENT(NAME customer, c.customer_name),
         XMLELEMENT(NAME total, o.amount)
       ) AS order_xml
FROM orders o
JOIN customers c USING (customer_id)
WHERE o.order_id = 1001;

Expected Output Using SQL XMLELEMENT

John Doe
Jane Smith
Acme Corp250.00

Use Cases with SQL XMLELEMENT

Serialize relational data to XML for APIs or file export.
Generate XML fragments inside SQL queries for downstream ETL.
Build nested XML documents that mirror object hierarchies.
Combine with XMLAGG to create XML arrays/lists.

Common Mistakes with SQL XMLELEMENT

Misspelling the NAME keyword or omitting it entirely.
Using spaces or invalid characters in element or attribute names.
Forgetting XMLATTRIBUTES() parentheses.
Assuming NULL values will appear; by default they are skipped.
Mixing text content and nested elements without comma separation.

First Introduced In

SQL:2003 (SQL/XML)

Frequently Asked Questions

What does XMLELEMENT return?

It returns a value of the XML data type containing the constructed element. In engines without XML types it may return CLOB/VARCHAR.

How do I include attributes?

Add an XMLATTRIBUTES clause: XMLATTRIBUTES(expr AS attr_name). Multiple attributes are comma-separated.

Can I nest XMLELEMENT calls?

Yes. You can place XMLELEMENT inside another XMLELEMENT to build complex, hierarchical XML documents.

How do NULLs behave?

Content expressions that evaluate to NULL are ignored. To force explicit nil attributes, use database-specific options like NULL ON NULL in PostgreSQL.