XML functions

Devart ODBC Driver for PostgreSQL supports the following XML functions and expressions for generating, querying, and exporting XML data.
They cover XML construction, predicates, XPath-based processing, and mapping tables or queries to XML and XML Schema.

Producing XML content

Function / Expression	Return type	Description
`xmltext(text)`	`xml`	Wraps a text value in an XML text node and escapes XML special characters.
`xmlcomment(text)`	`xml`	Creates an XML comment node. The content must not contain `--` or end with `-`.
`xmlconcat(xml, …)`	`xml`	Concatenates multiple XML fragments into a single XML value; `NULL` arguments are ignored.
`xmlelement(NAME name, …, content …)`	`xml`	Creates a new XML element with the specified name, optional attributes, and content.
`xmlforest(content AS name, …)`	`xml`	Builds a sequence (“forest”) of XML elements, each using its own name and content.
`xmlpi(NAME name [, content])`	`xml`	Creates an XML processing instruction; the content must not contain `?>`.
`xmlroot(xml, VERSION {text \| NO VALUE} [, STANDALONE {YES \| NO \| NO VALUE}])`	`xml`	Modifies the root node properties (version and standalone flag) of an existing XML value.
`xmlagg(xml)` (aggregate)	`xml`	Aggregates and concatenates XML values from multiple rows into a single XML fragment.

XML predicates

Expression / Function	Return type	Description
`xml IS DOCUMENT`	`boolean`	Returns `true` if the `xml` value is a well-formed XML document (single root element), not just a fragment.
`xml IS NOT DOCUMENT`	`boolean`	Returns `true` if the `xml` value is not a full document (it is an XML fragment).
`XMLEXISTS(text PASSING [BY REF] xml [BY REF])`	`boolean`	Evaluates an XPath expression against an XML value and returns `true` if the expression yields at least one node.
`xml_is_well_formed(text)`	`boolean`	Returns `true` if the input text is well-formed XML. Interpretation (document vs content) depends on the `xmloption` setting.
`xml_is_well_formed_document(text)`	`boolean`	Returns `true` if the input text is a well-formed XML document.
`xml_is_well_formed_content(text)`	`boolean`	Returns `true` if the input text is well-formed XML content (not necessarily a full document).

Processing XML

Function / Expression	Return type	Description
`xpath(xpath_expr text, xml [, nsarray text[]])`	`xml[]`	Evaluates an XPath 1.0 expression on an XML value and returns an array of matching XML nodes or values. Optional namespace mappings can be passed in `nsarray`.
`xpath_exists(xpath_expr text, xml [, nsarray text[]])`	`boolean`	Returns `true` if the XPath expression matches at least one node in the XML value; similar to `XMLEXISTS` but supports explicit namespace mappings.
`XMLTABLE([XMLNAMESPACES(...)], row_expression PASSING document_expression, COLUMNS …)`	`setof record`	Evaluates an XPath expression and projects the result into a set of rows and columns, mapping XML nodes and attributes to SQL columns.

Mapping tables and queries to XML

Function	Return type	Description
`table_to_xml(table regclass, nulls boolean, tableforest boolean, targetns text)`	`xml`	Exports the contents of a table as XML using the specified options for `NULL` handling, table/row layout, and target namespace.
`query_to_xml(query text, nulls boolean, tableforest boolean, targetns text)`	`xml`	Runs an SQL query and maps its result set to XML with configurable `NULL` handling, layout, and target namespace.
`cursor_to_xml(cursor refcursor, count integer, nulls boolean, tableforest boolean, targetns text)`	`xml`	Reads a defined number of rows from a cursor and exports them as XML.
`table_to_xmlschema(table regclass, nulls boolean, tableforest boolean, targetns text)`	`xml`	Generates an XML Schema (XSD) that describes the XML representation produced by `table_to_xml`.
`query_to_xmlschema(query text, nulls boolean, tableforest boolean, targetns text)`	`xml`	Generates an XSD schema for the XML output of `query_to_xml`.
`cursor_to_xmlschema(cursor refcursor, nulls boolean, tableforest boolean, targetns text)`	`xml`	Generates an XSD schema for the XML output of `cursor_to_xml`.
`table_to_xml_and_xmlschema(...)`	`xml`	Produces a combined XML document containing both table data and its associated XML Schema.
`query_to_xml_and_xmlschema(...)`	`xml`	Produces a combined XML document containing query results and the corresponding XML Schema.
`schema_to_xml(schema name, nulls boolean, tableforest boolean, targetns text)`	`xml`	Exports the data from all tables in a schema to XML.
`schema_to_xmlschema(...)`	`xml`	Generates an XML Schema for the XML representation of a database schema.
`schema_to_xml_and_xmlschema(...)`	`xml`	Exports schema data and the corresponding XML Schema in a single XML document.
`database_to_xml(nulls boolean, tableforest boolean, targetns text)`	`xml`	Exports the entire database contents to XML.
`database_to_xmlschema(nulls boolean, tableforest boolean, targetns text)`	`xml`	Generates an XML Schema for the XML representation of the entire database.
`database_to_xml_and_xmlschema(nulls boolean, tableforest boolean, targetns text)`	`xml`	Exports both data and XML Schema for the entire database in a single XML document.