Re: Problems with distinct

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От Owen Jacobson
Тема Re: Problems with distinct
Дата
Msg-id 144D12D7DD4EC04F99241498BB4EEDCC20D48B@nelson.osl.com
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Ответ на Problems with distinct  (Andreas Joseph Krogh <andreak@officenet.no>)
Список pgsql-sql
Andreas Joseph Krogh wrote:

> Any idea why this works:
>
> SELECT distinct(g.groupname), g.id, g.p_id FROM onp_group g,
> onp_group g2
> WHERE g.id IN(SELECT g2.id UNION SELECT group_id FROM
> onp_group_children WHERE
> child_id = g2.id)
> AND g2.id IN(1,2,109,105, 112);
>
> And not this:
>
> SELECT g.id, g.p_id, distinct(g.groupname) FROM onp_group g,
> onp_group g2
> WHERE g.id IN(SELECT g2.id UNION SELECT group_id FROM
> onp_group_children WHERE
> child_id = g2.id)
> AND g2.id IN(1,2,109,105, 112);

Distinct is an SQL keyword, not a function.  The former is exactly equivalent to

SELECT DISTINCT g.groupname, g.id, .... FROM ....

except that the first field is inside a (trivial) expression that makes it look like a function call.


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