Re: triggers: how to check if a field changed?

Messagewell, i wonder if this is really performant on large TEXT fields or if the compare costs as much as just running reindex for every update...

- thomas

----- Original Message -----
From: Lance Arlaus
To: pgsql-novice(at)postgresql(dot)org
Sent: Tuesday, August 30, 2005 6:25 AM
Subject: Re: [NOVICE] triggers: how to check if a field changed?

The following assumes you're writing the trigger in PL/pgSQL, but there are similar facilities in the other supported langs.

There are two records (OLD and NEW) that are pre-defined in trigger procedures. Simply compare the fields on those records.
For example (assuming field is non-nullable):

IF (OLD.p_msg_raw <> NEW.p_msg_raw) THEN
-- Reindex
ENDIF

Doc reference: http://www.postgresql.org/docs/8.0/interactive/plpgsql-trigger.html

-----Original Message-----
From: pgsql-novice-owner(at)postgresql(dot)org [mailto:pgsql-novice-owner(at)postgresql(dot)org] On Behalf Of me(at)alternize(dot)com
Sent: Monday, August 29, 2005 8:47 PM
To: pgsql-novice(at)postgresql(dot)org
Subject: [NOVICE] triggers: how to check if a field changed?

hi list

for our discussion board i've successfully set up a trigger to have tsearch2 index the record every time it is updated. this works fine, but also triggers the reindex of the record every time i update the "# of views" counter, which creates unnecessary load. in a trigger, is there a way to check the fields affected by the UPDATE query? i only want to have the tsearch2 index updated when the indexed field (p_msg_raw) changed...

this is the current trigger (straight following the tsearch2 guide):

CREATE TRIGGER "posts_ts_update" BEFORE INSERT OR UPDATE
ON "forum"."posts" FOR EACH ROW
EXECUTE PROCEDURE "public"."tsearch2"(idxfti, p_msg_raw);

thanks in advance,
thomas