The problem has never been selectivity... I'm still wondering how the heck the server will be able to do a seek on a search like this one :

WHERE(

Oct_1 = 72

AND (Oct_2>108 OR (Oct_2=108 AND Oct_3>10) OR(Oct_2=108 AND Oct_3=10 AND Oct_4>=2))

)

OR

Oct_1 = 73

AND (Oct_2<90 OR (Oct_2=90 AND Oct_3<=205) OR(Oct_2=90 AND Oct_3=205 AND Oct_4<=1))

)