From: felix@crowfix.com
To: pgsql-sql@postgresql.org
Subject: Delete with foreign keys
Date: Fri, 22 Feb 2008 10:00:21 -0800
Message-ID: <20080222180021.GA7700@crowfix.com> (raw)
I have three tables --
CREATE TABLE name (id INT PRIMARY KEY, str VARCHAR(20));
CREATE TABLE place (id INT PRIMARY KEY, name_id INT REFERENCES name(id));
CREATE TABLE data (id INT PRIMARY KEY, place_id INT REFERENCES place(id));
I want to delete all place and data rows which reference specific
names, but not the names themselves. I can do it like this:
DELETE FROM data d WHERE exists (SELECT id from place p WHERE d.place_id = p.id AND p.name_id IN (SELECT id FROM name WHERE str LIKE 'Fredonia%'));
DELETE FROM place WHERE name_id IN (SELECT id FROM name WHERE str LIKE 'Fredonia%');
but it seems rather roundabout, and I wonder whether the EXISTS and IN
business is slow. Is there some way to do it using JOINs? I think of
something like this:
DELETE FROM place p, name n WHERE p.name_id = n.id AND n.str LIKE 'Fredonia%';
but I don't want to delete the name rows. Then I think of this:
DELETE FROM place p WHERE p.name_id = name.id AND name.str LIKE 'Fredonia%';
but I feel uneasy about the two separate name references when the
table is not named in the FROM clause. Maybe that's just my novicity.
I also wonder about getting fancy and ending up with SQL specific to a
database; I don't have any plans to migrate, but I try to avoid
branding my SQL.
--
... _._. ._ ._. . _._. ._. ___ .__ ._. . .__. ._ .. ._.
Felix Finch: scarecrow repairman & rocket surgeon / felix@crowfix.com
GPG = E987 4493 C860 246C 3B1E 6477 7838 76E9 182E 8151 ITAR license #4933
I've found a solution to Fermat's Last Theorem but I see I've run out of room o
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To: pgsql-sql@postgresql.org
Cc: felix@crowfix.com
Subject: Re: Delete with foreign keys
In-Reply-To: <20080222180021.GA7700@crowfix.com>
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