DISTINCT and ORDER BY issue

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