SQL statement datetime issue

I have a sql statement that i am trying to use to tell me how many days one date is from another this should be either positive or negative number but I cant seem to get the data correct.  I end up with my created field being populated with other date time stamps.  

SELECT     OIBT.ItemCode, OIBT.BatchNum, POR1.ShipDate, POR1.OpenQty, OIBT.InDate, OPOR.CardCode, OPOR.CardName,
                      POR1.ShipDate - OIBT.InDate AS dayslate
FROM         OIBT INNER JOIN
                      OPDN ON OIBT.BaseType = OPDN.ObjType AND OIBT.BaseNum = OPDN.DocNum INNER JOIN
                      PDN1 ON OPDN.DocEntry = PDN1.DocEntry INNER JOIN
                      OPOR INNER JOIN
                      POR1 ON OPOR.DocEntry = POR1.DocEntry ON PDN1.BaseType = OPOR.ObjType AND PDN1.BaseEntry = OPOR.DocEntry AND
                      PDN1.BaseLine = POR1.LineNum
WHERE     (OPOR.U_SIF_PO_Sample = 'Y')


As you can see i take one datetime field and subtract it from another and want that to equal a number not datetime.
notasgoodasyouAsked:
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Patrick MatthewsConnect With a Mentor Commented:
If your date columns ALWAYS have "midnight" as the time portion:


SELECT     OIBT.ItemCode, OIBT.BatchNum, POR1.ShipDate, POR1.OpenQty, OIBT.InDate, OPOR.CardCode, OPOR.CardName, 
                      DATEDIFF(day, OIBT.InDate, POR1.ShipDate) AS dayslate
FROM         OIBT INNER JOIN
                      OPDN ON OIBT.BaseType = OPDN.ObjType AND OIBT.BaseNum = OPDN.DocNum INNER JOIN
                      PDN1 ON OPDN.DocEntry = PDN1.DocEntry INNER JOIN
                      OPOR INNER JOIN
                      POR1 ON OPOR.DocEntry = POR1.DocEntry ON PDN1.BaseType = OPOR.ObjType AND PDN1.BaseEntry = OPOR.DocEntry AND 
                      PDN1.BaseLine = POR1.LineNum
WHERE     (OPOR.U_SIF_PO_Sample = 'Y')

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Do keep in mind that DATEDIFF does **not** calculate the true elapsed time between two dates.  Rather, it returns the number of time period boundaries between two dates.  Thus, for

      DATEDIFF(year, Date1, Date2)

the function is looking for the number of **year boundaries** between the two dates and **not** the number
of full years that have passed.  If Date1 and Date2 are 01/08/1924 and  01/07/2007, then 83 year
boundaries are counted.

Similarly, if Date1 = 2009-12-31 23:59:59 and Date2 = 2010-01-01 00:00:00, even though only one second
elapsed, the function would *still* return a 1, because you have that year boundary.

Thus, if your dates do have real time portions, you may want to consider:


SELECT     OIBT.ItemCode, OIBT.BatchNum, POR1.ShipDate, POR1.OpenQty, OIBT.InDate, OPOR.CardCode, OPOR.CardName, 
                      DATEDIFF(second, OIBT.InDate, POR1.ShipDate) / 86400.0 AS dayslate
FROM         OIBT INNER JOIN
                      OPDN ON OIBT.BaseType = OPDN.ObjType AND OIBT.BaseNum = OPDN.DocNum INNER JOIN
                      PDN1 ON OPDN.DocEntry = PDN1.DocEntry INNER JOIN
                      OPOR INNER JOIN
                      POR1 ON OPOR.DocEntry = POR1.DocEntry ON PDN1.BaseType = OPOR.ObjType AND PDN1.BaseEntry = OPOR.DocEntry AND 
                      PDN1.BaseLine = POR1.LineNum
WHERE     (OPOR.U_SIF_PO_Sample = 'Y')

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Patrick
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Ephraim WangoyaConnect With a Mentor Commented:
use datediff
SELECT     OIBT.ItemCode, OIBT.BatchNum, POR1.ShipDate, POR1.OpenQty, OIBT.InDate, OPOR.CardCode, OPOR.CardName, 
                      DATEDIFF(DAY, POR1.ShipDate, OIBT.InDate) AS dayslate
FROM         OIBT INNER JOIN
                      OPDN ON OIBT.BaseType = OPDN.ObjType AND OIBT.BaseNum = OPDN.DocNum INNER JOIN
                      PDN1 ON OPDN.DocEntry = PDN1.DocEntry INNER JOIN
                      OPOR INNER JOIN
                      POR1 ON OPOR.DocEntry = POR1.DocEntry ON PDN1.BaseType = OPOR.ObjType AND PDN1.BaseEntry = OPOR.DocEntry AND 
                      PDN1.BaseLine = POR1.LineNum
WHERE     (OPOR.U_SIF_PO_Sample = 'Y')

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