Gather Statistics

How gather statistics improves performance of a query?

[QUOTE=soumabhal]How gather statistics improves performance of a query?[/QUOTE]


Hello, It helps if you include more details on what you are looking for... This is very broad question... Please be specific so some one can answer..

When one executes SQL what happens is the database converts the SQL into execution plan. Then the best choice of the possible way to extract is made. Among the number of alternatives say the index used to extract or etc the best choice is made which involves the cost optimization also. For this gather statistics is sued which in turn improves the performance.

I think there is a something called as dbms_stats package used for this purpose. Is it not? If I am wrong someone correct me?