Message-ID: <42C3D5E9.8010007@archonet.com>
Date: Thu, 30 Jun 2005 12:22:17 +0100
From: Richard Huxton <dev@archonet.com>
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To: Nick Stone <nick@harelane.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: SQL Query question
References: <20050630092944.E94022514BD@smtp.nildram.co.uk>
In-Reply-To: <20050630092944.E94022514BD@smtp.nildram.co.uk>
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Nick Stone wrote:
> Hi
> 
> Whilst I'm not new to SQL I am reasonably new to Postgres and as such I have
> a question on the following query:

> FROM
>     "Terms" As tbl1 LEFT JOIN
>     "SearchStore" As tbl2 ON tbl1."KeywordID" = tbl2."KeywordID" AND
> tbl2."StockID" = 1
> Why does the above query work fine and the folowing query not work? And as a
> additional kind of spanner in the works I've tried the following on MS SQL
> Server and Oracle both of which produce the correct results

> FROM
>     "Terms" As tbl1 LEFT JOIN
>     "SearchStore" As tbl2 ON tbl1."KeywordID" = tbl2."KeywordID"
> WHERE 
...
>     (tbl2."StockID" = 1)

Hmm - I'm not sure that MSSQL/Oracle are giving the "right" answer here. 
I assume the tbl2.stockid test is the issue here, and we apply the test 
after the join whereas the others push the condition inside the join.

I'm inclined to prefer PG's way of doing things, since it means you get 
what you explicitly asked for (to my point of view anyway). Not sure 
what the SQL spec says though, and in the end I suppose that's the only 
way to decide "right".

--
   Richard Huxton
   Archonet Ltd