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How does the xmltable function work in PostgreSQL?
In the SQL standard, the xmltable function evaluates expressions in the XML Query language, but PostgreSQL allows only XPath 1.0 expressions, as discussed in Section D.3.1. The mandatory COLUMNS clause specifies the list of columns in the output table. Each entry describes a single column. See the syntax summary above for the format.
What is the function XPath in PostgreSQL?
The function xpath evaluates the XPath 1.0 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. If the XPath expression returns a scalar value rather than a node-set, a single-element array is returned.
How does the XMLEXISTS function in PostgreSQL work?
The function xmlexists evaluates an XPath 1.0 expression (the first argument), with the passed XML value as its context item. The function returns false if the result of that evaluation yields an empty node-set, true if it yields any other value. The function returns null if any argument is null.
Can a by ref be used in PostgreSQL?
The BY REF and BY VALUE clauses are accepted in PostgreSQL, but are ignored, as discussed in Section D.3.2. In the SQL standard, the xmlexists function evaluates an expression in the XML Query language, but PostgreSQL allows only an XPath 1.0 expression, as discussed in Section D.3.1.
In the SQL standard, the xmltable function evaluates expressions in the XML Query language, but PostgreSQL allows only XPath 1.0 expressions, as discussed in Section D.3.1. The required COLUMNS clause specifies the column(s) that will be produced in the output table. See the syntax summary above for the format.
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.
When to use column name in PostgreSQL XML?
The example above shows that if the content value of the element is a column reference, column name is used by default. Else a name must be mentioned. Element names those are not valid XML names are escaped. if not type XML, content data is escaped to make valid XML content.
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.