What is an index in SQL?

Question

What is an index in SQL? Can you explain or reference to understand clearly?

Where should I use an index?

Answer 1

INDEX is a performance optimization technique that speeds up the data retrieval process. It is a persistent data structure that associated with a Table (or View) in order to increase performance during retrieving the data from that table (or View).

Index based search is applied more particularly when your queries include WHERE filter. Otherwise, i.e, a query without WHERE-filter selects whole data and process. Searching whole table without INDEX is called Table-scan.

You will find exact information for Sql-Indexes in clear and reliable way: follow these links:

1. For cocnept-wise understanding: http://dotnetauthorities.blogspot.in/2013/12/Microsoft-SQL-Server-Training-Online-Learning-Classes-INDEX-Overview-and-Optimizations.html
2. For implementation-wise understanding: http://dotnetauthorities.blogspot.in/2013/12/Microsoft-SQL-Server-Training-Online-Learning-Classes-INDEX-Creation-Deletetion-Optimizations.html