What are indexes in SQL?

Indexes are used to speed up performance of SQL queries. there are following indexes in database which are being used :

Index type

Clustered

Nonclustered

Unique

Index with included columns

Think about a book index.How easy it is to find a specific page in a book by the first page Index.

Almost the same concept applies here.We can add an index on a field or multiple fields in a database.

and that field will be found faster when searched.

It's always a good practice to add and index on a column or multiple columns on a database

It was just a very brief description of index.we have different  kinds of indexing mechanism like clustered,non clustered,unique,... which is out of the patience of this context

There Is More Than One Type Of Index's , and It's Hard To Explain All Of It In One Comment But Think Of It As a A Way Of Sorting The Data (To Be More Specific Columns ) So That The Engine Can Easily Find It By This Sort

So When You Request A Data From A Specific Column , SQL Server Will Know Where and How Exactly To Search,Find and Retrieve Your Data , Pretty Much Like Searching For a Topic in a Book Using The Book's Index , The Main Purpose Of Index Is To Improve Query Performance and Save Time  

indexe is a database object mainly used to improve the performance of SQL queries.

Indexs are of three types

1.Clustered index can be created manually or will be created by creating primary key.

2.Non-Clustered Index

3.Column Store Index introduced in 2012

Indexes are created to improve the performance of SQL queries. Indexed are used when the data is for SQL queries is huge and quick access is required.

Index is one of the object in sql server which needs to retrieve data from database more efficiently. Its like index of the book. It consist of two type 1. Clustered index 2. Non-Clustered Index. Clustered index is physically arranged the data in database so there is only one clustered index avialable in table and it saves the data in leaf level. While non- clustered index logically arranged the data and it can more than one in a table. It saves the pointer of the data to the leaf level. 

AN INDEX IS USED TO SPEED UP THE PERFORMANCE OF QUERIES.IT DOES THIS BY REDUCING THE NO. OF DATABASE DATA PAGE THAT HAVE TO BE VISITE/SCCANED.

An index is used to speed up searching in the database.

These are essential things to know for performence tuning.

There are clustered and non-clustered indexes.

clustered is used mostly

Index determines the physical order of the data in a table

For example, if you want to reference all pages in a book that discusses a certain topic, you first refer to the index, which lists all the topics alphabetically and are then referred to one or more specific page numbers.

An index helps to speed up SELECT queries and WHERE clauses, but it slows down data input, with the UPDATE and the INSERT statements. Indexes can be created or dropped with no effect on the data.