位图索引适用于什么情况?

不同值很少（现在可以支持5000个）,而且很少更新.

Bitmap indexes are more advantageous than B-tree indexes in certain situations:
• When a table has millions of rows and the key columns have low cardinality—that
is, there are very few distinct values for the column. For example, bitmap indexes
may be preferable to B-tree indexes for the gender and marital status columns of a
table containing passport records.
• When queries often use a combination of multiple WHERE conditions involving
the OR operator.
• When there is read-only or low update activity on the key columns.

A bitmap index is an indexing method added with Oracle V7.3 that can provide both performance benefits and storage savings. Bitmap indexes are particularly useful for data warehousing environments because data is usually updated less frequently and ad hoc queries are more common.

Bitmap INdex is only useful when you have a large number of records but few distinct value . It's very different from B-tree index .
If the table is updated frequently , you should not apply Bitmap Index on it .