query performance

Some people have already reacted, many thanks. To give some more information: SQLEXPLAIN shows that the index lst_date is taken. All other queries perform excellent, only this one is in trouble. To whom we do not really understand the problem: fst_date <= "1998-4-1" ...... LST_date >= "1998-4-1" Example (by fst_date index) fst_date lst_date ---------- ---------- 1998-3-30 1998-4-1 1998-3-30 1998-4-2 1998-3-30 1998-4-3 .... ..... 1999-4-1 1998-4-1 1998-4-1 1998-4-1 1998-4-2 1998-4-1 1998-4-2 ..... ...... 1999-4-1 1998-4-2 and so on. As you will see that an index will not be of much help. The column lst_date was added to the index to avoid lots of duplicate index entries: about 200 a day. If more information is required please let me know.