@Ann Harrison: Thanks for the detail explanation. so i guess i have the indexes correct.

@svein_erling: actually i'm trying to retrieve only one index. I forgot to put "first 1" on my first post.

I have done some more checking and found out that because i use join, the query wont use the descending index.

I did more testing and try these queries

"select col1 from table1 where col2=1 and col3=1 and col4=1 and col5=1"
and
"select col1 from table1 where col2>1 and col3>1 and col4=1 and col5=1"

index1 (col2, col3, col4, col5)
index2 (col4, col5)

query no 1 uses index no 1
and query no 2 uses index no 2.

Can you guys tell me what happen?