SQL CREATE INDEX

Index in SQL is a schema object utilized by servers to accelerate row retrieval by employing pointers, thus diminishing disk I/O. While they expedite select queries and WHERE clauses, they can impede data input, updates, and inserts. Index in SQL can be created or dropped without altering data, optimizing database performance. This article delves into index creation, deletion, and usage.

Create index in sql

Syntax

Here, "index_name" is the name assigned to the index, "table_name" is the name of the table on which the index is created, and "column_name" is the name of the column for which the index is applied.

Example

In this example:

• The index is named "idx_customer_id".
• It is created on the "Orders" table.
• The index is applied to the "customer_id" column.

For Multiple Columns

Syntax

Example

This creates an index in SQL named idx_name on the employees table with columns first_name and last_name. This index will help optimize queries that involve searching or sorting by both the first name and last name of employees.

For Unique Indexes

Syntax

This statement creates a unique index in SQL named idx_name on the specified table with the specified column. It ensures that each value in the indexed column is unique across all rows in the table.

Example

In this example, a unique index in SQL named idx_email is created on the email column of the employees table. This ensures that each email address stored in the email column is unique across all records in the employees table.

Removing an Index

You can remove an index from the data dictionary using the DROP INDEX command.

Syntax

Where "index_name" is the name of the index you want to drop.

Example

This command will remove the index named "idx_customer_name" from the table "customers".

Altering an Index

To alter an existing table's index by rebuilding or reorganizing it.

Syntax

In this syntax:

• index_name refers to the name of the index that needs to be modified.
• table_name is the name of the table where the index is defined.
• REBUILD is the keyword indicating that the index should be rebuilt.

Example

idx_customer_id is the name of the index on the Customers table that needs to be modified.

Confirming Indexes

You can verify the indexes existing within a specific table either designated by the user or by the server itself, along with their uniqueness.

Syntax

This query retrieves information about the indexes existing in the user's schema, including their names, types, uniqueness constraints, and other relevant details.

Example

Replace 'your_table_name' with the name of the table you want to check for indexes. This query will return information about all indexes associated with the specified table.

Renaming an Index

You have the option to utilize the system-stored procedure sp_rename to change the name of any index in SQL within the database.

Syntax

This procedure allows you to efficiently modify the name of an existing index.

Example

This command will rename the index from "idx_old" to "idx_new" in the specified table.

SQL Server Database

In SQL Server Database, the DROP INDEX command removes an existing index from a table. Here's the syntax:

Syntax

This command removes the index named "index_name" from the table named "table_name". Dropping an index can be useful if it's no longer needed or if you want to recreate it with different specifications.