Bitmap index is one of the index types that is supported by oracle. Unlike B*tree index, this is very compressed index. It means if I create a bitmap index on a column, then the generated index table will be smaller when compared the index table which is generated by the binary index on the same column. The reason is, in bitmap index, ROWIDs won’t be stored in the index table, instead index values will be mapped against bitmaps. Bitmap is nothing but it stores either of this values, 1(Match) or 0(No Match). For each distinct values in the column, a separate index record will be created. Unlike b*tree index, bitmap index can accept NULL and it creates separate index entry for this. Bitmap index will work better if number of distinct values are relatively less when compared to the total number of records. Why is it referred as “relatively less”? this index will work fine if table of 1,000,000,000 records contains 5000 distinct values and if table of 1,000 records contains 5 distinct va...
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