DECLARE @id_campaign UNIQUEIDENTIFIER;
SET @id_campaign = (SELECT MAX(ID) FROM [dbo].[Campagnes]);

DECLARE @compaign_start_date DATE;
DECLARE @compaign_end_date DATE;

DECLARE @YEAR INT;
DECLARE @MONTH INT;

SET @YEAR = (SELECT Annee - 1 FROM Campagnes WHERE ID = @id_campaign);
SET @MONTH = (SELECT 12 - NbMoisEditables FROM Campagnes WHERE ID = @id_campaign);

SET @compaign_start_date = DATEFROMPARTS(@YEAR, @MONTH, 1);
SET @compaign_end_date = DATEADD(DAY, -1, DATEADD(MONTH, 1, @compaign_start_date));

print 'Year - ' + CAST(@YEAR AS VARCHAR);
print 'Month - ' + CAST(@MONTH AS VARCHAR);
print 'Start date - ' + CAST(@compaign_start_date AS VARCHAR);
print 'End date - ' + CAST(@compaign_end_date AS VARCHAR);