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Editorial Team
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Asked: 2026-05-27T04:55:08+00:00

I have 2 table (pcgroup and client pc). Let say the date today is

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I have 2 table (pcgroup and client pc). Let say the date today is 24/11, I need to find which PC is online and which pc is not online for the last 2 days using only mySQL.

INSERT INTO pcgroup(id, groupName) 
  VALUES(1, 'defaultGroup');
INSERT INTO clientpc(id, pcGroupId, clientPcName, lastOnlineTime) 
  VALUES(1, 1, 'pc1', '2011-11-24');
INSERT INTO clientpc(id, pcGroupId, clientPcName, lastOnlineTime) 
  VALUES(2, 1, 'pc2', '2011-11-24');
INSERT INTO clientpc(id, pcGroupId, clientPcName, lastOnlineTime) 
  VALUES(3, 1, 'pc3', '2011-11-20');
INSERT INTO clientpc(id, pcGroupId, clientPcName, lastOnlineTime) 
  VALUES(4, 1, 'pc4', '2011-11-20');
INSERT INTO clientpc(id, pcGroupId, clientPcName, lastOnlineTime) 
  VALUES(5, 1, 'pc5', '2011-11-20');

Here is my query for now

SELECT DISTINCT
  pcgroup.id AS pcGroupID, pcgroup.groupName,
  online.onlinePC, offline.offlinePC
FROM
  (
    SELECT   
      pcgroup.Id, pcGroup.groupName
    FROM
      pcgroup
    WHERE
      (pcgroup.Id = 1)
  ) pcgroup
LEFT  JOIN
  (
    SELECT
      clientpc.Id, clientpc.pcGroupId, clientpc.clientPcName AS onlinePC
    FROM
      clientpc
    WHERE
      DateDiff(CURDATE(),clientpc.lastOnlineTime) <= 2
    AND
      DateDiff(CURDATE(),clientpc.lastOnlineTime) IS NOT NULL
  ) online  
 ON 
  pcgroup.Id = online.pcGroupId
 LEFT JOIN
   (
     SELECT
       clientpc.Id, clientpc.pcGroupId, clientpc.clientPcName AS offlinePC
     FROM
       clientpc
     WHERE
       (DateDiff(CURDATE(),clientpc.lastOnlineTime) > 2
     OR
        DateDiff(CURDATE(),clientpc.lastOnlineTime) IS NULL)
   ) offline 
  ON pcgroup.Id = offline.pcGroupId

This is the result I get

*pcGroupID    groupName        onlinePC       offlinePC*
  1           defaultGroup      pc1             pc3
  1           defaultGroup      pc1             pc4
  1           defaultGroup      pc1             pc5
  1           defaultGroup      pc2             pc3
  1           defaultGroup      pc2             pc4
  1           defaultGroup      pc2             pc5

However, what I need is something like this

*pcGroupID    groupName        onlinePC       offlinePC*
  1           defaultGroup      pc1             pc3
  1           defaultGroup      pc2             pc4
  1           defaultGroup                      pc5

So my question is, is that achievable? and if yes, how. Have been working on this query for 2 days. So i really appreciate if you guys can help me out.

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1 Answer

  1. Editorial Team

    Why not use 2 simple queries and do the presentation in your application?:

     --- Online ---
 SELECT
     c.pcGroupID, p.groupName, c.clientPcName, 'Online' AS pcStatus
 FROM
     pcgroup AS g
   JOIN
     clientpc AS c
       ON g.Id = c.pcGroupId
 WHERE
     g.Id = @pcGroupIdToBeChecked
   AND
     c.lastOnlineTime >= CURDATE() - INTERVAL 2 DAY

 --- Offline ---
 SELECT
     c.pcGroupID, p.groupName, c.clientPcName, 'Offline' AS pcStatus
 FROM
     pcgroup AS g
   JOIN
     clientpc AS c
       ON g.Id = c.pcGroupId
 WHERE
     g.Id = @pcGroupIdToBeChecked
   AND
     ( c.lastOnlineTime < CURDATE() - INTERVAL 2 DAY
      OR
       c.lastOnlineTime IS NULL
     )
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