Question

I have the following SQL:

DECLARE @ActualFromDT DATETIME,
        @ActualToDT DATETIME

IF (ManPowerUsage.FromDT >= Shift.FromDT)
    SET @ActualFromDT = ManPowerUsage.FromDT
ELSE
    SET @ActualFromDT =  Shift.FromDT

IF (ManPowerUsage.ToDT <= Shift.ToDT)
    SET @ActualToDT = ManPowerUsage.ToDT
ELSE
    SET @ActualToDT =  Shift.ToDT

SELECT Shift.ShiftID,
       Line.Line,
       ( SELECT SUM(DATEDIFF(MINUTE, @ActualFromDT, @ActualToDT))
              / DATEDIFF(MINUTE, Shift.FromDT, Shift.ToDT)

         FROM   ManPowerUsage

         WHERE  ManPowerUsage.LineID = Line.LineID
            AND ((Shift.FromDT < ManPowerUsage.FromDT AND Shift.ToDT > ManPowerUsage.FromDT) 
              OR (Shift.FromDT < ManPowerUsage.ToDT   AND Shift.ToDT > ManPowerUsage.ToDT  ))
            AND ManPowerUsage.IsEdited = 0
       ) AS ActualManpower
FROM ......

the command obviously doesn’t work but I would like to know how i to go about setting the parameters before I do the DATEDIFFs

Answer 1

Nowhere. You use the CASE expression for “inline IF”

SELECT Shift.ShiftID,
   Line.Line,
   ( SELECT SUM(DATEDIFF(MINUTE,
               CASE
                  WHEN ManPowerUsage.FromDT >= Shift.FromDT
                         THEN ManPowerUsage.FromDT
                  ELSE Shift.FromDT
               END,
               CASE
                  WHEN ManPowerUsage.ToDT <= Shift.ToDT
                         THEN ManPowerUsage.ToDT
                  ELSE Shift.ToDT 
               END))
          / DATEDIFF(MINUTE, Shift.FromDT, Shift.ToDT)
...