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Re: BUG #1540: Enhancement request: 'ambiguous' column reference

From: Richard Neill <rn214(at)hermes(dot)cam(dot)ac(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Richard Neill <postgresql(at)richardneill(dot)org>,pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #1540: Enhancement request: 'ambiguous' column reference
Date: 2005-03-14 23:18:27
Message-ID: 42361BC3.2030200@hermes.cam.ac.uk (view raw or flat)
Thread:
Lists: pgsql-bugs
Dear Tom and Neil,

Thanks very much for your help, and your explanations. This makes a lot 
of sense, and I agree - this bug is definitely invalid.

Best wishes

Richard




Tom Lane wrote:
> "Richard Neill" <postgresql(at)richardneill(dot)org> writes:
> 
>>SELECT instrument,priceband,pounds FROM tbl_instruments,tbl_prices WHERE
>>tbl_instruments.priceband=tbl_prices.priceband;
> 
> 
>>ERROR:  column reference "priceband" is ambiguous
> 
> 
>>I think that the first query ought to succeed, since although priceband is
>>ambiguous (it could mean either tbl_prices.priceband or
>>tbl_instruments.priceband), the information in the WHERE clause means that
>>they are explicitly equal, and so it doesn't matter which one we use.
> 
> 
> Doing that would be contrary to the SQL specification, AFAICS.
> 
> However, you can get the effect you want by writing the query like
> 
> SELECT instrument,priceband,pounds FROM
> tbl_instruments JOIN tbl_prices USING (priceband);
> 
> which both provides the join condition and logically merges the two
> input columns into just one output column.
> 
> 			regards, tom lane
> 

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