. . . "And just as you would typedef in C or create abstract types in C++, you create UDTs in SQL too.here is an example, using a useful testing date function that is cross-dialect, does not rely on any user-supplied function support, and can be incorporated into live code.-- postgresqlCREATE DOMAIN datetime_type timestamp null;create view system_datetime as select 1 as id, now() as date_now ;-- MS SQL serve" .