We use the sql INDEX as a way to optimize our database queries. A database administrator or data architect will usually assign an index to a specific column in a database table. As a result, the query performance is impacted.

We create a sql index to improve performance of a database table when running sql queries. An index can be created, modified, or deleted from a database table. We can review the following sql syntax for the creation, alteration, and removal of an index.

Create Index SQL Syntax

CREATE INDEX <index_name> ON <table_name> (<column_name>);

The syntax to create indexes on tables is pretty similar across most databases. If the above referenced syntax doesn’t work then refer to your database syntax documentation.

In the following example, we want to include an index on our id field in our customer table. We may or may not need to create indexes on id or key fields. This all depends on the database.

create index in sql

Altering Table Indexes

It’s easier to drop and recreate an index even though certain databases allow ALTER and MODIFY INDEX statements. ALTER INDEX is supported by Oracle, Microsoft SQL Server, and PostgreSQL. As a result, the ALTER INDEX command may offer limitations over dropping and recreating an index.

Deleting or Removing Table Indexes

DROP INDEX <index_name> ON <table_name>;

Removing indexes are fairly straight-forward. Also, our use-cases for tables and data may change over time. As a result, we may not need a certain index on a table anymore.

It’s important to note that removing an index can have a dramatic effect on database performance. This is especially true of more established databases. For example, the ones with several ETL process, procedures, views, and other types of queries.

create index multiple columns sql

We can quickly drop and recreate our index with new columns. An index does not need to be a single column. They can contain multiple columns. In conclusion, the use of a sql index is all defined by the types of queries being executed.