Thread: Trigger question
Hi there. I'm trying to use triggers for the first time, but I'm having some problems. Here's my SQL: create function set_counter() returns opaque as 'BEGIN new.count := 0; RETURN new; END;' language 'plpgsql'; create trigger set_counter after insert or update on nivel for each row execute procedure set_counter(); count is an int, and its default value is -1. The problem is that after I insert something, count value is still -1, not 0! Could someone tell me what's wrong? Thanks -- Nelio Alves Pereira Filho IFX Networks Sao Paulo / Brazil
Nelio Alves Pereira Filho <nelio@ifx.com.br> writes: > create trigger set_counter after insert or update on nivel > for each row execute procedure set_counter(); > The problem is that after I insert something, count value is still -1, > not 0! You want a BEFORE trigger, not an AFTER trigger. AFTER is too late to affect the contents of the stored row. regards, tom lane
I got it. But here's what I need to do: after any modification on the table, I must run a procedure that will do some calculation, and then set these values for each row. This calculation establishes relationships between rows, and builds logically a tree. To accomplish all that, first I need to unset some values, so I decided to use the BEFORE trigger to unset these values, and the AFTER trigger to do this calculation. Will I have to use explicit queries? And what's the real purpose of the AFTER trigger? Thanks Tom Lane wrote: > > Nelio Alves Pereira Filho <nelio@ifx.com.br> writes: > > create trigger set_counter after insert or update on nivel > > for each row execute procedure set_counter(); > > > The problem is that after I insert something, count value is still -1, > > not 0! > > You want a BEFORE trigger, not an AFTER trigger. AFTER is too late > to affect the contents of the stored row. > > regards, tom lane -- Nelio Alves Pereira Filho IFX Networks Sao Paulo / Brazil
Nelio Alves Pereira Filho <nelio@ifx.com.br> writes: > To accomplish all that, first I need > to unset some values, so I decided to use the BEFORE trigger to unset > these values, and the AFTER trigger to do this calculation. Why don't you just do all the work in the BEFORE trigger? > And what's the real purpose of the AFTER trigger? The sequence of events is compute contents of tuple to insert/update (per the query) apply BEFORE triggers check constraints insert tuple apply AFTER triggers You *must* use a BEFORE trigger if you want to alter the tuple that was computed by the query. The point of an AFTER trigger is that it won't be run until constraints have been passed, so you can avoid doing potentially expensive work until you know the tuple is good. You might use an AFTER trigger to propagate changes into other tables, for example. But you can't change the tuple. regards, tom lane
> > these values, and the AFTER trigger to do this calculation. > > Why don't you just do all the work in the BEFORE trigger? For instance, If I do an UPDATE inside a function that will be triggered by an UPDATE, won't it loop forever? Does PostgreSQL support recursive functions? Thanks