XML functions

[beikov]

The idea is to add some functions to query and manipulate XML.
Also see https://www.postgresql.org/docs/10/functions-xml.html

Construction

• xmlelement(name,v1[,vn]*) - constructor function that creates an xml element
• xmlattributes(k1,v1[,kn,vn]*) - constructor function that creates a xml attributes
• xmlcomment(comment) - constructor function that creates a xml comment
• xmlparse(payload) - parses an xml root

Query

• xmlagg(xml) within group (...) - aggregates xml elements into a xml forest
• xmlexists(xquery, xml) true if the XQuery expression in the first argument returns any nodes, and false otherwise
• xpath(xpath, xml) returns an array of xml values that match the XPath expression
• xpath_exists(xpath, xml) true if the XPath expression in the first argument returns any nodes, and false otherwise

Manipulation

• xmlconcat(xml, xml)

Track HHH-18497 for progress.