XML values

An XML value represents well-formed XML in the form of an XML document, XML content, or a sequence of XML nodes.

An XML value that is stored in a table as the value of a column that is defined with the XML data type must be a well-formed XML document. XML values are processed in an internal representation that is not comparable to any string value. The only predicates that can be applied to the XML data type are the XMLEXISTS predicate and the NULL predicate.

An XML value can be transformed into a serialized string value that represents the XML document by using the XMLSERIALIZE function. Similarly, a string value that represents an XML document can be transformed to an XML value by using the XMLPARSE function.

The XML data type has a variable length and allows for a wide range of sizes. Although data of this type has no defined maximum length, it does have an effective maximum length limit when treated as a serialized string value that represents XML. The maximum effective length is the same as the Db2 limit for a LOB data value. Db2 treats XML string data in a similar manner as LOB data to accommodate very large XML values. Thus, XML values are constrained by the same maximum length limit as LOB data. Unlike the LOB data type which has a LOB locator type, there is no XML locator type.

Restrictions when using XML values: With a few exceptions, you can use XML values in the same contexts in which you can use other data type. XML values cannot be used in the following contexts:
  • SELECT lists that are preceded by the DISTINCT clause
  • GROUP BY clauses
  • ORDER BY clauses
  • A subselect of a fullselect with a set operator that is not UNION ALL
  • Basic predicates, quantified predicates, BETWEEN predicates, DISTINCT predicates, IN predicates, or LIKE predicates
  • Aggregate functions with the DISTINCT keyword
  • Primary, unique, or foreign keys
  • CREATE TYPE statements

No host languages have any built-in support for an XML data type.