I have a table with 1498587 rows. The users query this data by year, and to improve this query I created a index on year, but the query didn't use this index because of the uniqueness of this index. Therefore I decided to create a bitmap index, but the query still doesn't use the bitmap index. Why?
This show how many records for each year.
ACT_YEAR COUNT(*)
---------- ----------
93 21858
94 168088
95 169920
96 163749
97 168262
98 180296
99 185229
2000 202371
2001 197180
2002 13665
27969