Question

I’m working on selecting data in a database and I’m not sure how to proceed.

I need to select the latest update

My tables look like this:

datatable: userid, userinfo, updated (timestamp);
usertable: userid, username, realname, email, userNumber, Org, SN, Dept.

There can be multiple entries in datatable for each user. For this query I only need the latest entry for each user from datatable:

SELECT datatable.userid, 
       datatable.userinfo, 
       datatable.updated, 
       usertable.username 
  FROM datatable 
  JOIN usertable ON datatable.userid = usertable.userid 
 WHERE (....)

Answer 1

Use:

SELECT d.userid, 
       d.userinfo, 
       d.updated, 
       u.username 
  FROM datatable d
  JOIN usertable u ON u.userid = d.userid
  JOIN (SELECT t.userid,
               MAX(t.updated) AS max_updated
          FROM DATATABLE t
      GROUP BY t.userid) x ON x.userid = d.userid
                          AND x.max_updated = d.updated