How about DELETE FROM T1 WHERE T1.PK IN (SELECT T1.PK FROM T1 EXCEPT SELECT T2.FK FROM T2);
Mel On Tue, Oct 20, 2009 at 7:59 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Shaul Dar <shaul...@gmail.com> writes: > > I assume this will work but will take a long time: > > > DELETE * FROM T1 where T1.PK NOT IN > > (SELECT T1.PK FROM T1, T2 where T1.PK = T2.FK) > > Well, yeah, but it's unnecessarily inefficient --- why not just > > DELETE FROM T1 where T1.PK NOT IN > (SELECT T2.FK FROM T2) > > However, that still won't be tremendously fast unless the subselect fits > in work_mem. As of 8.4 this variant should be reasonable: > > DELETE FROM T1 where NOT EXISTS > (SELECT 1 FROM T2 where T1.PK = T2.FK) > > Pre-8.4 you should resort to the "left join where is null" trick, > but there's no need to be so obscure as of 8.4. > > regards, tom lane > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance >
