UDF don't give the same result - sql

Question

when I exececute the UDF out of the trigger the result is not the same
the UDF return always true when executing in the trigger
but out of the trigger the result is true or false
ALTER FUNCTION [dbo].[MandatExist]
(
#Numero int,
#IdBranche int,
#Exercice int
)
RETURNS bit
AS
BEGIN
DECLARE #Result bit
DECLARE #Nbr int
DECLARE #Categ int
SELECT #Categ = CategorieNumero
FROM Branche
WHERE IdBranche = #IdBranche
SELECT #Nbr=COUNT(*)
FROM Mandat AS M INNER JOIN Branche AS B ON M.IdBranche=B.IdBranche
WHERE (Numero = #Numero) AND (B.CategorieNumero = #Categ) AND (Exercice = #Exercice)
IF #Nbr = 0
SET #Result = 0
ELSE
SET #Result = 1
RETURN #Result
END
the trigger call MandatExist to get if the number exist or not
ALTER TRIGGER [dbo].[ValidInsertUpdate_Mandat]
ON [dbo].[Mandat]
FOR INSERT,UPDATE
AS
BEGIN
SET NOCOUNT ON;
DECLARE #Cloturer AS bit
DECLARE #Exercice AS int
DECLARE #IdBranche AS int
DECLARE #Numero AS int
DECLARE #Message AS nvarchar(100)
SELECT #Cloturer=Cloturer, #Exercice=Exercice, #Numero=Numero, #IdBranche=IdBranche
FROM INSERTED
IF (dbo.MandatExist(#Numero, #IdBranche, #Exercice)=1)
BEGIN
SET #Message = 'Numero de mandat existant.'
RAISERROR(#Message, 16, 1)
ROLLBACK TRAN
END

Answer 1

INSERTED is a table, thus may contain more than one row which means that this code
SELECT #Cloturer=Cloturer, #Exercice=Exercice, #Numero=Numero, #IdBranche=IdBranche
FROM INSERTED
is essentially incorrect.
UDFs are not the best choice for set-based programming and may cause performance degradation. Specifically this UDF makes absolutely no sense, has no reason for encapsulating this code into separate module. This is a trivial EXISTS code.
Entire function can and must be replaced by EXISTS statement, the whole code of the trigger might look like:
IF EXISTS(
SELECT 1
FROM INSERTED
INNER JOIN ...
WHERE ...
)
BEGIN
RAISERROR(...)
END
I'm not sure what's the meaning of your tables and columns, but I assume you are trying to check some uniqueness. So, assuming that you don't want another Mandat record for the same CategorieNumero, the final EXISTS might look like:
IF EXISTS(
SELECT 1
FROM INSERTED i
INNER JOIN Branch b on b.IdBranche = i.IdBranch
-- other branches with the same CategorieNumero; why isn't CategorieNumero unique?
INNER JOIN Branch b_dup on b_dup.CategorieNumero = b.CategorieNumero
-- existing Mandat rows for the same CategorieNumero with any IdBranch
INNER JOIN Mandat m_dup on m_dup = b_dup.IdBranch
-- ensure you're not comparing inserted/updated Mandat row to itself
WHERE i.ID != m_dup.ID
)
...
But your intent is unclear to me and I think that after clarification most of your needs will be easily satisfied by unique constraints.
If you don't want more that one row for each set of (Exercice, Numero, IdBranch) - just add a unique constraint to Mandat table and drop both trigger and function!
Don't overuse triggers. And UDFs.

Answer 2

i have used the solution of Ivan
IF EXISTS(
SELECT 1
FROM INSERTED I INNER JOIN Branche b ON b.IdBranche = i.IdBranche
INNER JOIN Branche b_dup ON b_dup.IdBranche = b.IdBranche
INNER JOIN Mandat m_dup on (m_dup.Exercice = i.Exercice) AND (m_dup.Numero = i.Numero) AND (b_dup.IdBranche=i.IdBranche)
WHERE i.IdMandat != m_dup.IdMandat
)
BEGIN
RAISERROR('error', 16, 1)
ROLLBACK TRAN
END