This statement is ANSI SQL:2011 compliant, but includes non-ANSI Teradata extensions.
The requirement that parentheses appear when the argument list is empty is a Teradata extension to preserve compatibility with existing applications.
Additionally, when a statement specifies an ambiguous expression that can be interpreted as a UDF invocation or a method invocation, Teradata Database gives UDF invocation higher precedence over method invocation. ANSI SQL:2011 gives method invocation higher precedence over UDF invocation.