Grant Morgan wrote:
I am having a problem with left joins in Postgresql.(probably my
misunderstanding of left joins)
My first Query returns
70,000
select count(*)
from h
where h.tn > 20
and h.tn < 30
my left join
returns only 34,000
select count(*)
from h left join p using (r,pos)
where h.tn > 20
and h.tn < 30
and p.r_order=1
since it is a left join I though I should get a number no smaller in the
left join than the original unjoined query.
You don't. You make the left join, then apply another condition
"p.r_order=1". If you want to demonstrate a problem, you'll need to make
sure the queries are the same.
--
Richard Huxton
Archonet Ltd
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