Bitmap Index

Conditions for using bitmap indexes essentialy are the low cardinality of the indexed columns with low selectivity, which means huge amout of retrieved rows.

What is "low cardinality" in this context. Yes, a GENDER or YES/NO column is easy to understand. But what about attributes with 20 or 30 different values. Where is the break even point in comparison with b-tree indexes.

Thanks in advance

Marcel Romahn Received on Wed Feb 18 1998 - 00:00:00 CST