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special integrity constraints

From: Erik Thiele <erik(at)thiele-hydraulik(dot)de>
To: pgsql-sql(at)postgresql(dot)org
Subject: special integrity constraints
Date: 2004-03-22 09:20:31
Message-ID: 20040322102031.6a6f0b77.erik@thiele-hydraulik.de (view raw or flat)
Thread:
Lists: pgsql-docspgsql-sql
hi,

i have two tables

create table a (x integer);
create table b (y real);

i have the special constraint that the sum of the number of rows in
table a plus the number of rows in table b must be even.

so there is a posibility of adding one element to a and one element to
b, and again the constraint is met.

but this of course does not work, since between adding the element to a
and adding the element to b, the constraint is not met.

so i cannot use a trigger.

what i need is the execution of a check procedure at commit time. is
that somehow possible?

my database has much more tables than just a and b, and most time the other
tables are modified and not a or b, so it would be nice to execute the
constraint checking procedure only if a or b was modified.

yes :) this question i asked in my former mail too, but I think it
looked like there was a workaround and my problem was wrong. so i
created this new kind of problem here to make things clearer.


cu
Erik


-- 
Erik Thiele

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