Regarding Index on Table

[Ravi Kumar Ravuru]

Hello All,
I would like to know that the effect of index on the table.What does if we create index on the table?Please throw some light on me regarding this and refer some links related to it.
Thanks in Advance.
Ravi

[Mark Spritzler]

Well for the most part an index is supposed to speed querying the table up. An index stores pointers to rowids. So if you have a where clause that uses a field that is indexed, it can find the match in the index and then use the pointer to fetch the rows.
Whereas if there is no index, a query will have to do a table scan, meaning it will go through each and every record and check to see if each record matches the criteria.
Hope this is close.
Mark