What is Index in SQL?

An index is a special data structure in SQL for tables. We use Indexes for SQL operations like SELECT query, DELETE, UPDATE. Indexes help to fast these operations and manipulate from the table. Indexes are just like a column or columns in the table.

How to Create Index in SQL?

There are many queries are available in SQL to use or create an index in your table. The basic syntax for creating an index in SQL is given below:

CREATE INDEX index_name
ON table_name ( column1 , column2 , . . . ) ;

Above is the simple syntax for the index in a table. But in the above index, there is no restriction on duplicate values.

Below is a query for unique value in a table. Means every record of this table will unique according to its primary key.

CREATE UNIQUE INDEX index_name
ON table_name ( column1 , column2 , . . . ) ;

Example of Index in SQL

A simple example of Index in SQL is given below:

                                CREATE INDEX websites_idx

                                ON websites ( site_name , server ) ;

For unique Index:

                                CREATE UNIQUE INDEX websites_idx

                                ON websites ( site_name ) ;

How to Create Index in SQL Server (2012, 2014 and 2017)

A complete query for creating a simple index system in your SQL database is given below:

CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name

    ON 

    ON <object> ( column [ ASC | DESC ] [ ,…n ] )

    [ INCLUDE ( column_name [ ,…n ] ) ]

    [ WHERE <filter_predicate> ]

    [ WITH ( <relational_index_option> [ ,…n ] ) ]

    [ ON { partition_scheme_name ( column_name )

         | filegroup_name

         | default

         }

    ]

    [ FILESTREAM_ON { filestream_filegroup_name | partition_scheme_name | ‘ NULL ‘ } ]

sss[;]

< object > :: = { database_name.schema_name.table_or_view_name | schema_name.table_or_view_name | table_or_view_name }

<relational_index_option> ::= {

    PAD_INDEX = { ON | OFF }

  | FILLFACTOR = fillfactor

  | SORT_IN_TEMPDB = { ON | OFF }

  | IGNORE_DUP_KEY = { ON | OFF }

  | STATISTICS_NORECOMPUTE = { ON | OFF }

  | STATISTICS_INCREMENTAL = { ON | OFF }

  | DROP_EXISTING = { ON | OFF }

  | ONLINE = { ON | OFF }

  | RESUMABLE = {ON | OF }

  | MAX_DURATION = <time> [MINUTES]

  | ALLOW_ROW_LOCKS = { ON | OFF }

  | ALLOW_PAGE_LOCKS = { ON | OFF }

  | OPTIMIZE_FOR_SEQUENTIAL_KEY = { ON | OFF}

  | MAXDOP = max_degree_of_parallelism

  | DATA_COMPRESSION = { NONE | ROW | PAGE}

     [ ON PARTITIONS ( { <partition_number_expression> | <range> }

     [ , …n ] ) ]

}

<filter_predicate> ::= <conjunct> [ AND <conjunct> ]

<conjunct> ::= <disjunct> | <comparison>

<disjunct> ::= column_name IN (constant ,…n)

<comparison> ::= column_name <comparison_op> constant

<comparison_op> ::= { IS | IS NOT | = | <> | != | > | >= | !> | < | <= | !< }

<range> ::= <partition_number_expression> TO <partition_number_expression>

How do you create an index?

An index lists the terms and topics that are discussed in a document, along with the pages that they appear on. To create an index, you mark the index entries by providing the name of the main entry and the cross-reference in your document, and then you build the index.

Why do we create index in SQL?

The CREATE INDEX statement is used to create indexes in tables. Indexes are used to retrieve data from the database more quickly than otherwise. The users cannot see the indexes, they are just used to speed up searches/queries.

How do I create a full text index in SQL Server?

To create a full text index choose your table and right click on that table and select “Define Full–Text Index” option. Now select Unique Index. It is compulsory that for “Full Text Index” table must have at least one unique index. Select columns name and language types for columns.