Question

What are the main advantages of indexing the tables on SQL Server 2008?

Please explain with examples (if possible)..

Thanks

Answer 1

Indexing provides a way to improve the performance of your data access queries. Suppose you have a table with different identifying columns. Putting an index on each column, or combinations of columns that are queried together will improve your response time.

Example: you have a User table with columns:

FirstName | LastName | ZipCode

Put an index on LastName if you are querying on last name, such as:

SELECT * FROM User where LastName = 'SMITH'

Index could be:

CREATE NONCLUSTERED INDEX [MyIndex] ON [User] 
(
    [LastName] ASC
) WITH (
    PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, 
    SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, 
    ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON
) 
ON [PRIMARY]

Or, put an index on 2 columns if you are querying these columns together:

SELECT * FROM User where LastName = 'SMITH' and ZipCode = '14222'

Index could be:

CREATE NONCLUSTERED INDEX [MyIndex] ON [User] 
(
    [LastName] ASC,
    [ZipCode] ASC
) WITH (
    PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, 
    SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, 
    ONLINE = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON
) 
ON [PRIMARY]

All else equal, your queries will be faster if you create the index. Be careful though, too many indices may actually decrease performance.