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What is an Index in SQL?

An index in SQL is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional space and decreased performance on data modification operations. It essentially provides a quick lookup of data based on the values of certain columns.

Syntax of CREATE INDEX Statement:

The syntax for creating an index in SQL is as follows:

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

Steps to Create an Index:

  1. Identify the Table and Columns: Determine the table and columns on which you want to create the index.
  2. Choose a Name for the Index: Provide a unique name for the index.
  3. Write the SQL Statement: Compose the CREATE INDEX statement with the identified index name and columns.
  4. Execute the SQL Statement: Run the SQL statement to create the index.

Example Scenarios:

Let’s go through a few scenarios to understand the CREATE INDEX statement better.

Scenario 1: Creating an Index on a Single Column

Suppose we have a table named employees with columns employee_id, name, and department_id, and we want to create an index on the employee_id column.

CREATE INDEX idx_employee_id
ON employees (employee_id);

Scenario 2: Creating an Index on Multiple Columns

Now, let’s create an index on multiple columns, say department_id and name columns, in the employees table.

CREATE INDEX idx_department_name
ON employees (department_id, name);


  • In Scenario 1, we created an index named idx_employee_id on the employee_id column of the employees table. This index will enhance the retrieval speed of records based on the employee_id.
  • In Scenario 2, we created an index named idx_department_name on both department_id and name columns of the employees table. This composite index can be used to speed up queries that involve both department and employee name filtering.


Understanding how to use the CREATE INDEX statement in SQL is crucial for optimizing database performance. By creating appropriate indexes on columns frequently used in queries, you can significantly enhance the speed of data retrieval operations. However, it’s essential to strike a balance between index usage and the overhead it incurs during data modification operations.

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