15.10 - Example: Valid Use of Subquery in WHEN Clause - Teradata Database

The following CREATE TRIGGER request succeeds because its WHEN clause aggregate function is specified as part of a subquery:

Note that the aggregate subquery is on the right hand side of the inequality condition, as it must be.

     CREATE TRIGGER trigwhen3
       BEFORE INSERT ON t1
       REFERENCING OLD AS previous 
     FOR EACH ROW 
       WHEN (previous.a <= (
         SELECT SUM(b)
         FROM t2, t3 
         WHERE t2.c = t3.c))
     ABORT;