SQL Server 2008 :: FEFO Query If Condition

I wish to make a query with if condition Implemented in a database sql server 2008 R2.

I would like to set up a system FEFO (first expired first out) based on batch number based on the dates of Lapsed but since I struggle to put my request in place. The principle of my request is:

if amount of movement (QTEMVT)> = amount entered by the user via a user interface then withdraws the amount entered by the user in the batch (NUMLOT) the amount of movement of the item that lapses the first (execution of my request).
else if amount of movement (QTEMVT) <amount entered by the user
then the difference between the amount entered by the user and the amount of movement (QTEMVT) (execution of my request) and the following conditions:
the amount of movement (QTEMVT) = the amount of movement (QTEMVT) of this item stored in my database and the amount of movement (QTEMVT) <> 0
by taking the difference of the item requested directly from the batch (NUMLOT) of the item directly after lapses.

Basically I want to set up an item management query based on batch number and expiration dates.

ps: QTEMVT = quantity of the item stored in my database
NUMLOT = batch number items
DATFABRIC = manufacturing date items
DATPEREMP = expiry date items

Here is my request:

SELECT f.NUMLOT,f.DATFABRIC,f.DATPEREMP,f.QTEMVT
FROM FAIRE f INNER JOIN mouvement m ON f.CODMVT = m.CODMVT
INNER JOIN TYPE_MOUVEMENT tm ON tm.CODTYPMVT = m.CODTYPMVT
INNER JOIN SOUS_SITE ss ON ss.CODSOUSIT = m.CODSOUSIT
INNER JOIN SITE s ON s.CODSITE = ss.CODSITE

[Code] ....