Question

I’m a postgresql user and I’m trying to follow this :
http://www.postgresql.org/docs/current/interactive/sql-createtrigger.html

CREATE TRIGGER check_update 
    BEFORE UPDATE ON accounts 
    FOR EACH ROW 
    WHEN (OLD.balance IS DISTINCT FROM NEW.balance) 
    EXECUTE PROCEDURE check_account_update(); 

but with AFTER instead of BEFORE. and I’m keep getting error on or near WHEN.
does that because i have to use BEFORE ? what if i need to execute the procedure after updating column and it has really changed ?

Answer 1

PostgreSQL 8.4 doesn’t support WHEN with triggers, from the fine manual:

Synopsis

CREATE TRIGGER name { BEFORE | AFTER } { event [ OR ... ] }
ON table [ FOR [ EACH ] { ROW | STATEMENT } ]
EXECUTE PROCEDURE funcname ( arguments )

There is no WHEN there. You can put the WHEN logic inside your trigger function:

if old.balance is not distinct from new.balance then
    return new;
end if;
-- The rest of the trigger...

or upgrade to at least PostgreSQL 9.0 and use WHEN when creating the trigger.