Hi, I have a table that contains data for electric motors the format is:

DATE(DateTime) | TagName(VarChar(50) | Val(Float) |

2009-11-03 17:44:13.000 | Motor_1 | 123.45

2009-11-04 17:44:13.000 | Motor_1 | 124.45

2009-11-05 17:44:13.000 | Motor_1 | 125.45

2009-11-03 17:44:13.000 | Motor_2 | 223.45

2009-11-04 17:44:13.000 | Motor_2 | 224.45

Data for each motor is inserted daily, so there would be 31 Motor_1s and 31 Motor_2s etc. We do this so we can trend it on our control system displays. I am using views to extract last months max val and last months min val. Same for this months data. Then I join the two and calculate the difference to get the actual run hours for that month. The "Val" is a nonresetable Accumulation from a PLC(Controller). This is my query for Last months Max Value:

SELECT     TagName, Val AS Hours
FROM         dbo.All_Data_From_Last_Mon AS cur
WHERE     (NOT EXISTS
                          (SELECT     TagName, Val
                            FROM          dbo.All_Data_From_Last_Mon AS high
                            WHERE      (TagName = cur.TagName) AND (Val > cur.Val)))

This is my query for Last months Max Value:

SELECT     TagName, Val AS Hours
FROM         dbo.All_Data_From_Last_Mon AS cur
WHERE     (NOT EXISTS
                          (SELECT     TagName, Val
                            FROM          dbo.All_Data_From_Last_Mon AS high
                            WHERE      (TagName = cur.TagName) AND (Val < cur.Val)))

This is the query that calculates the difference and runs a bit slow:

SELECT  dbo.Motors_Last_Mon_Max.TagName, STR(dbo.Motors_Last_Mon_Max.Hours - dbo.Motors_Last_Mon_Min.Hours, 12, 2) AS Hours
FROM    dbo.Motors_Last_Mon_Min RIGHT OUTER JOIN
            dbo.Motors_Last_Mon_Max ON dbo.Motors_Last_Mon_Min.TagName = dbo.Motors_Last_Mon_Max.TagName

I know there is a better way. Ultimately I just need last months total and this months total. Any help would be appreciated.

Thanks in advance