rajsrinu

 Profile Answers by rajsrinu 

• Dec 12th, 2006

 

index works for fast retriving data. and it will not allows duplicates you can use index on column(s) not on tables

sibgatullah

• Dec 13th, 2006

 

effective use of index will speed up your query execution time.

ashok rajagopal

• Dec 14th, 2006

 

This is how the index works in simple terms.

When you add a row to a table, the rowid of that row plus a few other info is store in a separate area which is dedicated to keep it.  Lets say you define a unique index. When you insert a valid row, the rowid + the key of the index is stored in the index region ( i forgot what it's called physically ).  So a repository which says for this key, so and so is the rowid, is created.  When you try to fetch out the row containing that key, SQL engine looks into this region, finds out the rowid and moves to that location.

Things work pretty much the same way for all the type of indexes.  For a non unique index, it will be a single key and a number of rowids.  That means, for this key(or group of keys), all these rowids are possible. SQL engine takes this info, and goes to find out those particular rowids.