From: | "Josh Berkus" <josh(at)agliodbs(dot)com> |
---|---|
To: | Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk>, "pgsql-sql" <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: multiple lookup per row |
Date: | 2001-07-20 14:41:22 |
Message-ID: | web-88697@davinci.ethosmedia.com |
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Thread: | |
Lists: | pgsql-sql |
Gary,
First: Go out and buy "SQL for Smarties". Now. Read it.
However, I'll give you this one as a freebie:
> I've got a table 'phones' which has an indexed key 'pid' of type
> int4, and a
> phone number of type varchar(12).
>
> I've then got a table 'members' which as an index key 'mid' of type
> int4.
SELECT members.mid, members.name, members.address, hp.phone AS
home_phone, wp.phone AS work_phone, cp.phone as cell_phone
FROM members LEFT OUTER JOIN
(SELECT mid, phone FROM phones WHERE ptype = 'home') hp
ON members.mid = hp.mid
LEFT OUTER JOIN
(SELECT mid, phone FROM phones WHERE ptype = 'work') wp
ON members.mid = wp.mid
LEFT OUTER JOIN
(SELECT mid, phone FROM phones WHERE ptype = 'cell') cp
ON members.mid = cp.mid
ORDER BY members.name;
You're experiencing the usual problem encountered by procedural
programmers when they first start on SQL. SQL is a declarative
language, and requires a different knid of thinking than procedural
languages. Thus the use of table aliasing and subselects above.
Have fun!
-Josh
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Josh Berkus
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