From: | Gerardo Herzig <gherzig(at)fmed(dot)uba(dot)ar> |
---|---|
To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: statement-level trigger sample out there? |
Date: | 2007-11-29 19:18:02 |
Message-ID: | 474F106A.5080107@fmed.uba.ar |
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Lists: | pgsql-sql |
Stephen Cook wrote:
> I am curious (coming from a MS SQL Server background, I just started
> playing with PostgreSQL recently).
>
> What type of situation would warrant a statement-level trigger that
> can't access the old and new values? Without that access, isn't the
> only information you get is the fact that an operation occurred on the
> table? Or am I missing something?
>
> -- Stephen
What about this. Suppose you have this table "planets":
planet_name | star_id|....
There is a lot of stars, right? And if a very common query involves a
"select planet_name, count(*) from planets group by star_id"....Well, if
there is 1.000.000.000 of galaxies, and 1.000.000.000.000 of stars per
galaxy...Thats a lot of planets to count!!! So maybe you want a helper
table who maintains such of subtotals.
Well, each time you discover a new galaxy, insert every planet in the
monster table, and *after* all the inserts, run a trigger for updating
the helper table.
Cheers.
Gerardo
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