MS SQL update/insert query

Hello experts, Im newbie to MS SQL. I have two tables both hold the same fields Time, computer name, MAC, IP and Status which can be either logon or logoff. Table1 is populated by a logon script and Table2 should read and maintain from table1 only the first and last time a user logged on\off to any workstation.  
 I have written the following query which update only the last time a user logged on and off. I would like to refine it so it would also keep the first time a user logged on/off and insert a new record if username and computer name is not matching.  I set max pts as this is needed asap. Thanks

UPDATE Table2
   SET username = Table1.username
     , computer = Table1.computer
	 , status = Table1.status
	 , IP = Table1.IP
	 , MAC = Table1.MAC
	 , Time01 = Table1.time01
 FROM Logonoff2
 JOIN Table1
   ON Table2.username = logonoff_all.username 
	and Table12.computer = Table1.computer 
	and Table1.status = Table2.status
	and Table1.time01 > Table2.time01 
	
INSERT INTO Table2 (Username, Computer, Status, IP, time01)
  SELECT Table1.username, Table1.computer, Table1.status
	, Table1.IP, Table1.time01
  FROM Table1
 WHERE NOT EXISTS ( SELECT null FROM Table1
WHERE         Table2.userName = Table2.username 
	and computer.Table2 = Table1.computer)

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HAKSAAsked:
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pcelbaConnect With a Mentor Commented:
Let suppose the unique key in T_2 table is username + computer + status (I would prefer username + MAC + status but it does not matter).

You have to group records from T_1 always to avoid duplicities in T_2. And we may suppose both min and max time may change:

SELECT username, computer, IP, MAC, status, MIN(Time01) FirstTime, MAX(Time01) LastTime
  INTO #TempTime
  FROM T_1
 GROUP BY username, computer, IP, MAC, status 
 
UPDATE T_2
   SET Firsttime = CASE WHEN T_2.FirstTime < #TempTime.FirstTime THEN T_2.FirstTime ELSE #TempTime.FirstTime END,
       Lasttime  = CASE WHEN T_2.LastTime > #TempTime.LastTime THEN T_2.LastTime ELSE #TempTime.LastTime END
 FROM T_2
 JOIN #TempTime 
   ON T_2.username = #TempTime.username 
	and T_2.computer = #TempTime.computer 
	and T_2.status = #TempTime.status
 
INSERT INTO T_2
SELECT username, computer, IP, MAC, status, FirstTime, LastTime
  FROM #TempTime
 WHERE NOT EXIST 
   (SELECT null FROM T_2 
     WHERE username = #TempTime.username 
       AND computer = #TempTime.computer
       AND status = #TempTime.status)
 
DROP TABLE #TempTime

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pcelbaCommented:
It should be much easier to have two Time columns in Table2:
SELECT username, computer, IP, MAC, status, MIN(Time01) FirstTime, MAX(Time01) LastTime
  INTO Table2
  FROM Table1
 GROUP BY username, computer, IP, MAC, status

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pcelbaCommented:
If you need just one pair of time values independently on status, then you may remove status column from above select. If the status is important then you may use following:
SELECT t1.username, t1.computer, t1.IP, t1.MAC, 
       t1.FirstTime, t1min.Status FirstStatus, t1.LastTime, t1max.Status LastStatus
  FROM (SELECT username, computer, IP, MAC, MIN(Time01) FirstTime, MAX(Time01) LastTime
          FROM Table1
         GROUP BY username, computer, IP, MAC) t1
  INNER JOIN Table1 t1min ON t1min.username = t1.username AND t1min.MAC = t1.MAC AND t1min.Time01 = t1.FirstTime
  INNER JOIN Table1 t1max ON t1max.username = t1.username AND t1max.MAC = t1.MAC AND t1max.Time01 = t1.LastTime

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HAKSAAuthor Commented:
Hi pcelba,
thanks for your reply. I agree with you having 2 time columns in t2 made it much easier but I still have one small problem. Considering that t1 is a transition table and it will be cleaned up or regular bases,  How can I maintain the min (time) in t2 even after the original record is deleted in t1.
UPDATE T_2
   SET username = T_1.username
     , computer = T_1.computer
	 , status	= T_1.status
	 , IP = T_1.IP
	 , MAC= T_1.MAC
	 , Firsttime= (select min(Time01) from T_1)
	 , Lasttime = (select max(time01) from T_1)
 FROM T_2
 JOIN T_1
   ON T_2.username = T_1.username 
	and T_1.computer = T_1.computer 
	and T_1.status = T_2.status

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pcelbaCommented:
OK, this means you cannot create T_2 by one SELECT command but you have to go back to Insert/Update scenario. Then it should be sufficient to update just max time because the min time cannot change once calculated. It, of course, depends on the way how data are stored in T_1.
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pcelbaCommented:
WHERE NOT EXISTS   of course

Other possible solution exist, as well.
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HAKSAAuthor Commented:
It works just like i want it. Thanks
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