string-expression
A SELECT statement. The expression whose data type is to be queried must appear in the SELECT list. If the string is
not a valid SELECT statement, NULL is returned.
integer-expression
The position in the SELECT list of the desired expression. The first item in the SELECT list is numbered 1. If the integer-expression
value does not correspond to a SELECT list item, NULL is returned.
For user-defined domains, EXPRTYPE returns the description of the underlying data type, not the domain name. For example,
suppose you create a domain, mydomain, and define a table column using mydomain, as follows: