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Message-ID: <3F6CD6E9.5030005@houle.org>
Date: Sat, 20 Sep 2003 18:38:33 -0400
From: Kevin Houle <kevin@houle.org>
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To: Thilak babu <thilakbabu@siptech.co.in>
Subject: Re: Reg: Firing Trigger when a particular column value get changed
References: <63970.192.168.64.193.1063969270.squirrel@mail2.siptech.co.in>
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Thilak babu wrote:
>   I have a scnerio as to fire a trigger when i update a particular column
> in a table. Please do help me out in getting thro this.

The trigger function can use logic to exclude cases where a particular
column does not change. For example:

CREATE FUNCTION "column_update" () RETURNS TRIGGER AS '
   BEGIN
     IF ( NEW.column <> OLD.column ) THEN
       do-your-stuff-here;
     END IF;
   RETURN NEW;
END; ' LANGUAGE 'plpgsql';

CREATE TRIGGER "tg_column_update"
   BEFORE UPDATE ON "table_name"
   FOR EACH ROW EXECUTE PROCEDURE "column_update" ();

The trigger fires on every update, but the procedure doesn't do
anything unless the particular column changes. I don't think a
trigger can be defined to fire on anything more granular than a
table operation.

Kevin