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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