Date: Wed, 30 Jul 2014 15:45:24 -0700 (PDT)
From: David G Johnston <david.g.johnston@gmail.com>
To: pgsql-sql@postgresql.org
Message-ID: <1406760324275-5813363.post@n5.nabble.com>
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 <CAAvgTTT02zxdRzfcFiq+V-zDQzcOUNrsQGSLNsi2Xc02kuygKg@mail.gmail.com>
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 <CAAvgTTT02zxdRzfcFiq+V-zDQzcOUNrsQGSLNsi2Xc02kuygKg@mail.gmail.com>
Subject: Re: Reg: Sql Join
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CrashBandi wrote
> Hi,
> 
> I am having the following question. I am not sure how to approach it.
> Please help!
> 
> table A
>  name col1 col2 col3 col4  apple 100 11111 1 APL  orange 200 22222 3 ORG
> carrot 300 33333 3 CRT
> 
> table B
>   custom_name value obj_type obj_id  apple a FR 100  orange o FR 200 
> carrot
> c VG 300  apple d FR 11111  orange e VG 22222  carrot f UC 33333  apple h
> VG
> 1  orange o FR 3  carrot c VG 3
> when obj_type ='FR' then join on col1
> When obj_type='VG' then join on col2
> When obj_type='UC' then join on col2
> 
> Thanks In advance,
> CB

You cannot do conditional joins in this manner.  You will need to write
three joins, one each against a subquery with the appropriate where clause.

David J.


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