From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200211020407.gA2474Y12040@candle.pha.pa.us>
Subject: Re: select syntax question
In-Reply-To: <1036186412.25294.2.camel@Monet>
To: Wei Weng <wweng@kencast.com>
Date: Fri, 1 Nov 2002 23:07:04 -0500 (EST)
Cc: pgsql-sql@postgresql.org
MIME-Version: 1.0
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Yes, a big difference.  The first returns the distinct COUNT values, but
there is only one, of course.  The second returns the number of distinct
values in the column.

---------------------------------------------------------------------------

Wei Weng wrote:
> This is what is on postgresql's manual page:
> 
> http://www.postgresql.org/idocs/index.php?sql-select.html
> 
> SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
>     * | expression [ AS output_name ] [, ...]
>     [ FROM from_item [, ...] ]
>     [ WHERE condition ]
>     [ GROUP BY expression [, ...] ]
>     [ HAVING condition [, ...] ]
>     [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]
>     [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
>     [ FOR UPDATE [ OF tablename [, ...] ] ]
>     [ LIMIT { count | ALL } ]
>     [ OFFSET start ]
> 
> According to this syntax, SELECT DISTINCT COUNT(ID) FROM test
> should be valid while SELECT COUNT(DISTINCT ID) FROM test otherwise.
> 
> while in fact, both are valid.
> 
> Is there any difference between this two queries?
> 
> Thanks!
> 
> 
> -- 
> Wei Weng
> Network Software Engineer
> KenCast Inc.
> 
> 
> 
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