A scalar UDF can be invoked from both the SET clause and the WHERE clause of an UPDATE request. See Example: UPDATE Using an SQL UDF Invocation in the SET and WHERE Clauses.
|Clause||Usage rules are the same as those for invoking a scalar UDF from the …|
|SET||Select list of a SELECT request.
You must use the alias to reference the result of a scalar UDF invocation that has an alias.
|WHERE||WHERE clause of a SELECT request.
The scalar UDF must be invoked from within an expression that is specified as the search condition. Otherwise, the system returns an error.
See WHERE Clause.