Contents
What is the function of xmlconcat in PostgreSQL?
The function xmlconcat concatenates a list of individual XML values to create a single value containing an XML content fragment. Null values are omitted; the result is only null if there are no nonnull arguments. XML declarations, if present, are combined as follows.
How to extract value of XML tag in PostgreSQL?
You’d have to cast to text first: unknown_type_col::text::xml. Better to cast to ::xml right away. This has been tightened with PostgreSQL 9.1 (I think). Older versions were more permissive. Either way, with any of these methods the string has to be valid xml or the cast (implicit or explicit) will raise an exception.
How is XML formatted in PostgreSQL documentation 9.1?
Element content, if specified, will be formatted according to its data type. If the content is itself of type xml, complex XML documents can be constructed. For example: Content of other types will be formatted into valid XML character data. This means in particular that the characters <, >, and & will be converted to entities.
Is there an XMLEXISTS construct in PostgreSQL?
Also note that the SQL standard specifies the xmlexists construct to take an XQuery expression as first argument, but PostgreSQL currently only supports XPath, which is a subset of XQuery.
What is the function XPath in PostgreSQL?
To process values of data type xml , PostgreSQL offers the functions xpath and xpath_exists, which evaluate XPath 1.0 expressions. The function xpath evaluates the XPath expression xpath (a text value) against the XML value xml. It returns an array of XML values corresponding to the node set produced by the XPath expression.
When does XMLEXISTS return true in PostgreSQL?
The function xmlexists returns true if the XPath expression in the first argument returns any nodes, and false otherwise. (If either argument is null, the result is null.) The BY REF clauses have no effect in PostgreSQL, but are allowed for SQL conformance and compatibility with other implementations.
How is XML data converted to relational data?
Your XML data is complex and nested, and difficult to map to a relational schema. Mapping your XML format to a relational schema leads to a large number of tables. Your XML Schema is highly variable or tends to change over time. Your primary goal is to manage XML documents as intact business objects.