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Re: subselect prob in view

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: subselect prob in view
Date: 2004-06-21 14:19:43
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-sql
Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk> writes:
>      from requests r, users u, request_types t, 
>           request_states s, dealerships d, departments de, customers c
>           left outer join (select co_r_id, count(co_r_id) from comments group 
> by co_r_id) co on
>             co.co_r_id = r.r_id
> psql:goole1.sql:45: ERROR:  Relation "r" does not exist

I think you have learned some bad habits from MySQL :-(

PostgreSQL follows the SQL spec and makes JOIN bind more tightly than
comma.  Therefore, in the above the LEFT JOIN is only joining "c" to
"co" and its JOIN ON clause can only reference those two relations.

You could get the behavior you seem to expect by changing each comma
in the from-list to CROSS JOIN.  Then the JOINs all bind left-to-right
and so "r" will be part of the left argument of the LEFT JOIN.

Note that if you are using a pre-7.4 release this could have negative
effects on performance --- see the user's guide concerning how explicit
JOIN syntax constrains the planner.

			regards, tom lane

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