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May 8th, 2008, 05:35 PM

benbun

Contributing User

Join Date: Jan 2001

Posts: 44

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Query Help

I am having trouble getting a query to work.

I have a table along the following columns

ID | DATE | USER | DATA

The table has many rows, with each user having between 0 and many entries per day.

I want a query that returns the latest 50 records based on DATE, but I only want the latest entry for each USER.

I can obviously use a query along the lines of

SELECT * from table-name ORDER BY date DESC

but that would return many records for each USER, how can I limit so I get a maximum of 1 record per user ( i.e. their latest one )

any help appreciated

thanks

May 8th, 2008, 06:58 PM

r937

SQL Consultant

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Code:

SELECT d.id
     , d.date
     , d.user
     , d.data
  FROM ( SELECT user
              , MAX(date) as maxdate
           FROM daTable
         GROUP
             BY user ) AS u
INNER
  JOIN daTable AS d
    ON d.user = u.user   
   AND d.date = u.maxdate
ORDER
    BY d.date DESC LIMIT 50

__________________
r937.com | rudy.ca

May 9th, 2008, 02:37 AM

benbun

Contributing User

Join Date: Jan 2001

Posts: 44

Time spent in forums: 13 h 5 m 3 sec
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Hi R937

Thanks for the query, it looks impressive.

I am trying to break the query down so I can learn for the future. I don't understand why the JOIN is required. It looks to me like

Code:

SELECT user , MAX(date) as maxdate
  FROM daTable
 GROUP  BY user

will do it by itself.

What am I missing here ?

Thanks again

May 9th, 2008, 02:59 AM

benbun

Contributing User

Join Date: Jan 2001

Posts: 44

Time spent in forums: 13 h 5 m 3 sec
Reputation Power: 8

Oh, I see it now - the subquery finds the latest date for a user, the JOIN pulls back the record with the latest date found in the first query.

I am still left with one slight glitch, if a user has multiple records on a date then the join brings back all of them - I want a maximum of one record per user.

thanks

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