Question

I have a table of data as follows

id    status    conversation_id    message_id    date_created
1     1         1                  72            2012-01-01 00:00:00
2     2         1                  87            2012-03-03 00:00:00
3     2         2                  95            2012-05-05 00:00:00

I want to get all the rows from the table in date_created DESC order, but only one row per conversation_id. So in the case of the example data above, I would want to get the rows with id 2 and 3.

Any advice is much appreciated.

Answer 1

See SQL Fiddle

SELECT T.*
FROM T
WHERE NOT EXISTS (
  SELECT * 
  FROM T AS _T
  WHERE _T.conversation_id = T.conversation_id
  AND (
    _T.date_created > T.date_created
    OR
    _T.date_created = T.date_created AND _T.id > T.id) 
)
ORDER BY T.date_created DESC

gets

ID      STATUS  CONVERSATION_ID   MESSAGE_ID    DATE_CREATED
3         2         2                95         May, 05 2012 
2         2         1                87         March, 03 2012