From: Florian Weimer <fweimer@bfk.de>
To: pgsql-sql@postgresql.org
Subject: Deleting rows from a table not contained in another table
Date: Thu, 04 Mar 2010 10:51:17 +0000
Message-ID: <82eik04axm.fsf@mid.bfk.de> (raw)
I want to reimplement
DELETE FROM foo;
INSERT INTO foo SELECT * FROM bar;
in a way which does not touch rows which are not modified (mainly to
avoid locking issues). I've come up with this:
DELETE FROM foo WHERE NOT EXISTS
(SELECT * FROM bar WHERE foo.* IS NOT DISTINCT FROM bar.*);
INSERT INTO foo SELECT * FROM bar EXCEPT SELECT * FROM foo;
The problem is that the plan for the DELETE doesn't look pretty at all:
QUERY PLAN
-----------------------------------------------------------------------
Nested Loop Anti Join (cost=313.36..181568.96 rows=1 width=6)
Join Filter: (NOT (foo.* IS DISTINCT FROM bar.*))
-> Seq Scan on foo (cost=0.00..293.05 rows=20305 width=38)
-> Materialize (cost=313.36..516.40 rows=20305 width=32)
-> Seq Scan on bar (cost=0.00..293.05 rows=20305 width=32)
(5 rows)
Is there some way to turn this into a merge join, short of introducing
primary keys and using them to guide the join operation?
--
Florian Weimer <fweimer@bfk.de>
BFK edv-consulting GmbH http://www.bfk.de/
Kriegsstraße 100 tel: +49-721-96201-1
D-76133 Karlsruhe fax: +49-721-96201-99
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To: pgsql-sql@postgresql.org
Cc: fweimer@bfk.de
Subject: Re: Deleting rows from a table not contained in another table
In-Reply-To: <82eik04axm.fsf@mid.bfk.de>
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