DB Index

Clustered Index 


Clustered Index :-

1.There can be only one Clustered index for a table

2.usually made on the primary key

3.the logical order of the index matches the physical stored

order of the rows on disk



Non-Clustered Index

1.There can be only 249 Clustered index for a table

2.usually made on the any key

3.the logical order of the index does not match the physical

stored order of the rows on disk

Bitmap index

From Wikipedia, the free encyclopedia

Jump to: navigation , search

A bitmap index is a special kind of database index that uses bitmaps .

Bitmap indexes have traditionally been considered to work well for data such as gender, which has a small number of distinct values, e.g., male and female, but many occurrences of those values. This would happen if, for example, you had gender data for each resident in a city. Bitmap indexes have a significant space and performance advantage over other structures for such data. However, some researchers argue that Bitmap indexes are also useful for unique valued data which is not updated frequently.^[1] Bitmap indexes use bit arrays (commonly called "bitmaps") and answer queries by performing bitwise logical operations on these bitmaps