Indexes

Index

Indexes on a col actually arranges the data in the col in asc order and store there row's address. Without index, once the query  executed, the control goes to the table but with the indexes on, it goes to the index. Index is 2-dim table- data(ordered form) and rowid(physical address of each rec).      

Types

Simple Index - single col. create index idx_sal on EMP(sal); Composite Index - multiple col Unique Index - unique col only Reverse Index - data(ordered in desc) Function Based Index -  Bit-Map -