From: Hannu Krosing <hannu@tm.ee>
To: terry@greatgulfhomes.com
Cc: Postgres (E-mail) <pgsql-docs@postgresql.org>
Subject: Re: DISTINCT and ORDER BY issue
Date: 23 May 2002 23:17:32 +0500
Message-ID: <1022177854.10286.7.camel@rh72.home.ee> (raw)
In-Reply-To: <001401c20268$fdff0c40$2766f30a@development.greatgulfhomes.com>
References: <001401c20268$fdff0c40$2766f30a@development.greatgulfhomes.com>
On Thu, 2002-05-23 at 19:49, terry@greatgulfhomes.com wrote:
> I know what I am doing wrong: The order by needs to match the DISTINCT
> fields.
>
> Here's what I am doing: Get the 10 most recent applications user has used
> to put in their "recently used" menu.
>
> So I need to ORDER BY user_app_access_log.access_stamp DESC
>
> But I want each record distinct, eg if the last 5 hits were all for the same
> app, I want 1 record returned for that. So if I put the access_stamp field
> in the DISTINCT field set, then I go back to getting repeats of apps, hence
> not 10 unique app names...
>
> I wonder if there is a way to use an aggregate function to just return the
> first value, (ignoring the rest of the group), and use the group by clause
> on the app_name?
>
> Any ideas is appreciated.
>
> Here is my query/error message:
> Error while executing the query; ERROR: For SELECT DISTINCT, ORDER BY
> expressions must appear in target list
>
>
> SELECT DISTINCT applications.app_name, applications.app_long_name,
> applications.app_url, user_access.in_new_window
> FROM applications, user_access, user_app_use_log
> WHERE user_app_use_log.user_id = '1'
> AND user_app_use_log.app_name != 'index'
> AND user_access.app_name = user_app_use_log.app_name
> AND user_access.user_id = user_app_use_log.user_id
> AND user_access.division_id = 'GGH'
> AND applications.app_name = user_access.app_name
> ORDER BY user_app_use_log.access_stamp DESC
> LIMIT 10"
You can try either
SELECT DISTINCT app_name,app_long_name,app_url,in_new_window
FROM (
SELECT
user_app_use_log.access_stamp,
applications.app_name,
applications.app_long_name,
applications.app_url,
user_access.in_new_window
FROM applications, user_access, user_app_use_log
WHERE user_app_use_log.user_id = '1'
AND user_app_use_log.app_name != 'index'
AND user_access.app_name = user_app_use_log.app_name
AND user_access.user_id = user_app_use_log.user_id
AND user_access.division_id = 'GGH'
AND applications.app_name = user_access.app_name
ORDER BY user_app_use_log.access_stamp DESC
) t
LIMIT 10
;
or
SELECT
applications.app_name,
applications.app_long_name,
applications.app_url,
user_access.in_new_window,
max(access_stamp) as max_access_stamp
FROM applications, user_access, user_app_use_log
WHERE user_app_use_log.user_id = '1'
AND user_app_use_log.app_name != 'index'
AND user_access.app_name = user_app_use_log.app_name
AND user_access.user_id = user_app_use_log.user_id
AND user_access.division_id = 'GGH'
AND applications.app_name = user_access.app_name
GROUP BY 1,2,3,4
ORDER BY max_access_stamp DESC
LIMIT 10
;
and see which one is more effective
---------------
Hannu
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To: pgsql-docs@postgresql.org
Cc: hannu@tm.ee, terry@greatgulfhomes.com
Subject: Re: DISTINCT and ORDER BY issue
In-Reply-To: <1022177854.10286.7.camel@rh72.home.ee>
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