Help with MySQL query that is based on the number of clicks on an item

Question

I have a table setup like this (simplified for example):

user_id
item_id
click_dt

Each item_id has many user_id's. Basically it's storing the clicks on items, associated to a user_id.

I want to query through this and list only the latest user_id for each item_id, based on click_dt.

So if there are 5 clicks for item_id 55, the last click or click_dt DESC would be the record to show....

Make sense? Any help would be awesome... thanks!

Answer 1

Use:

SELECT x.*
  FROM YOUR_TABLE x
  JOIN (SELECT t.item_id,
               MAX(t.click_dt) AS max_date
          FROM YOUR_TABLE t
      GROUP BY t.item_id) y ON y.item_id = x.item_id
                           AND y.max_date = x.clicked_dt

Alternate:

SELECT x.item_id,
       x.user_id,
       x.click_dt
  FROM (SELECT t.item_id,
               t.user_id,
               t.click_dt,
               CASE
                 WHEN @item = t.item_id THEN @rownum := @rownum + 1
                 ELSE @rownum := 1
              END AS rk,
              @item := t.item_id
         FROM YOUR_TABLE t
         JOIN (SELECT @rownum := 0, @item := 0) r
     ORDER BY t.itemid, click_dt DESC) x
 WHERE x.rk = 1

Answer 2

Try this:

SELECT user_id,item_id,click_dt FROM
(
    SELECT MAX(click_dt) AS LastClick_dt,item_id FROM aTable
    GROUP BY item_id
) As LastClick
INNER JOIN aTable 
ON aTable.itemid = LastClick.item_id
AND aTable.click_dt = LastClick.LastClick_dt

The subselect part will give the latest click for each item_id, and then you can join this to the original table to retrieve the matching user_id.