Types of indexes Database index

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1 types of indexes

1.1 bitmap index
1.2 dense index
1.3 sparse index
1.4 reverse index





types of indexes
bitmap index

a bitmap index special kind of indexing stores bulk of data bit arrays (bitmaps) , answers queries performing bitwise logical operations on these bitmaps. commonly used indexes, such b+ trees, efficient if values index not repeat or repeat small number of times. in contrast, bitmap index designed cases values of variable repeat frequently. example, sex field in customer database contains @ 3 distinct values: male, female or unknown (not recorded). such variables, bitmap index can have significant performance advantage on commonly used trees.


dense index

a dense index in databases file pairs of keys , pointers every record in data file. every key in file associated particular pointer record in sorted data file. in clustered indices duplicate keys, dense index points first record key.


sparse index

a sparse index in databases file pairs of keys , pointers every block in data file. every key in file associated particular pointer block in sorted data file. in clustered indices duplicate keys, sparse index points lowest search key in each block.


reverse index

a reverse key index reverses key value before entering in index. e.g., value 24538 becomes 83542 in index. reversing key value particularly useful indexing data such sequence numbers, new key values monotonically increase.








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