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I cannot understand why the following two queries differ so much in
executi=
on time (almost ten times)
Query A (two queries)
select distinct moment.mid from moment,timecard where parent =3D 45 and
(pi=
d=3D17 and timecard.mid =3D moment.mid) order by moment.mid;
select distinct moment.mid from moment,timecard where parent =3D 45 and
(pb=
ar =3D 0) order by moment.mid;
Query B (combining the two with OR)
select distinct moment.mid from moment,timecard where parent =3D 45 and
((p=
id=3D17 and timecard.mid =3D moment.mid) or (pbar =3D 0)) order by
moment.m=
id;
$ time psql -o /dev/null -f query-a.sql fektest
real 0m2.016s
user 0m1.532s
sys 0m0.140s
$ time psql -o /dev/null -f query-b.sql fektest
real 0m28.534s
user 0m1.516s
sys 0m0.156s
I have tested this in two different computers with different amount of
RAM, fast or slow CPU, and the difference is persistent, almost ten
times.
I should say that this is on postgresql 7.4.16 (debian stable).
Can query B be rewritten so that it would execute faster?
TIA
--=20
Hans Ekbrand (http://sociologi.cjb.net)
<hans@[EMAIL PROTECTED]
>
GPG Fingerprint: 1408 C8D5 1E7D 4C9C C27E 014F 7C2C 872A 7050 614E
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