Example: Valid Use of Subquery in WHEN Clause - Advanced SQL Engine - 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;