Re: Reg: Sql Join

From: David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: Reg: Sql Join
Date: 2014-07-30 22:45:24
Message-ID: 1406760324275-5813363.post@n5.nabble.com
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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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