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Can triggers update other tables?

From: Rikard <rikard(dot)bosnjakovic(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Can triggers update other tables?
Date: 2011-10-20 00:24:42
Message-ID: b3a6792a-f980-4210-a816-4635feb3fce8@f13g2000vbv.googlegroups.com (view raw or flat)
Thread:
Lists: pgsql-novice
VERSION = 'PostgreSQL 8.4.2 on i686-pc-linux-gnu, compiled by GCC gcc
(GCC) 3.4.6, 32-bit'

I'm reading at http://www.postgresql.org/docs/8.4/static/sql-createtrigger.html
and http://www.postgresql.org/docs/8.4/static/plpgsql.html but I
cannot solve this problem. The very outline is that I'm having two
tables (in reality there are a lot more), something like this:

  SUMMARY ( id integer, num_stores integer; );
  ITEMS ( id serial PRIMARY KEY; name text; some_reference integer,
some_value smallint; ).

When a row is inserted in ITEMS, I want to launch a trigger that
issues a "UPDATE num_stores SET num_stores=(SELECT count(*) FROM items
WHERE id = <trigger_table.id>) where id = <trigger_table.id>".
Triggers seem to be run on functions returning plpgsql and I don't
know how to issue ordinary SQL-commands in SQL, so I don't know how to
reference these two tables in a single trigger.

Is it possible? If yes, which section of the manual is the place for
me to read up on?

Responses

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