>>Hi,
>>
>>How do you SUM number of days difference between two DateTime type fields as following:
>>
>>

>>select SUM( DATETIME1 - DATETIME2) AS NUMDAYS
>>

>
>It should work the way it's

I got:
Operand data type datetime is invalid for sum operator.
Because DATETIME1 - DATETIME2 is also datetime.

DECLARE @Test TABLE (Fld1 datetime, Fld2 datetime)
DECLARE @i int
SET @i = 0
WHILE @i < 20
      BEGIN 
         INSERT INTO @Test VALUES (GETDATE()+@i, GETDATE()+@i*20)
         SET @i = @i +1
      END
SELECT SUM(Fld2-Fld2) FROM @Test