Select distinct values from two columns

Question

I have a table with the following structure:

itemId  | direction | uid | created
133           0        17   1268497139
432           1        140  1268497423
133           0        17   1268498130
133           1        17   1268501451

I need to select distinct values for two columns - itemId and direction, so the output would be like this:

itemId  | direction | uid | created
432           1        140  1268497423
133           0        17   1268498130
133           1        17   1268501451

In the original table we have two rows with the itemId - 133 and direction - 0, but we need only one of this rows with the latest created time.

Thank you for any suggestions!

Answer 1

Use:

SELECT t.itemid,
       t.direction,
       t.uid,
       t.created
  FROM TABLE t
  JOIN (SELECT a.itemid,
               MAX(a.created) AS max_created
          FROM TABLE a
      GROUP BY a.itemid) b ON b.itemid = t.itemid
                          AND b.max_created = t.created

You have to use an aggregate (IE: MAX) to get the largest created value per itemid, and join that onto an unaltered copy of the table to get the values associated with the maximum created value for each itemid.