Database performance can be greatly affected by the proper use of indexes. They are one of the first objects you should investigate when encountering performance problems. However, you should remember that placing an index on a column may not necessarily provide the desired remedy. In those cases, you will commonly need to explore other performance tools.
Indexes are primarily used for two reasons:
To ensure the uniqueness of the indexed column’s values
To enhance performance
An index is an ordered set of records that correspond to records in a table. The index record consists of a column that relates to a corresponding column in the associated table. Each index record also has a rowid value, which is the location of the desired table ...