Salut,
Ce code peut aider
declare @d date
SELECT @d='20060722'
SELECT dateadd(day,
case when datepart(dw, @d) = 1 then -6
when datepart(dw, @d) = 7 then -5
else -7
end, @d)
source :
http://www.developpez.net/forums/d185758/bases-donnees/sybase/t-sql-jours-ouvr-s-operation-dates/