SQL DROP INDEX

What is SQL DROP INDEX?

Removes an existing index from a table, freeing storage and eliminating its maintenance overhead.

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Compatible dialects for SQL DROP INDEX: Supported by PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, SQLite (version 3.8.0+), IBM Db2, and most other relational databases.

SQL DROP INDEX Full Explanation

SQL DROP INDEX permanently deletes an index object. Once executed and committed, the index definition, its on-disk structures, and its statistics are removed. Query planners will no longer consider that index when generating execution plans. In PostgreSQL, the command can include IF EXISTS to avoid errors if the index is absent and CASCADE to drop objects (such as materialized views) that depend on it. The operation requires exclusive lock on the index and may briefly block concurrent DML. Dropping an index that backs a PRIMARY KEY or UNIQUE constraint is not allowed; use ALTER TABLE ... DROP CONSTRAINT instead. Because rebuilding a large index can be time-consuming, a common workflow is to DROP INDEX before bulk loads and recreate it afterward. In production, always verify that no critical queries rely on the index before removing it.

SQL DROP INDEX Syntax

-- PostgreSQL
DROP INDEX [CONCURRENTLY] [IF EXISTS] index_name [, ...] [CASCADE | RESTRICT];

-- MySQL
DROP INDEX index_name ON table_name [ALGORITHM = DEFAULT | INPLACE | COPY] [LOCK = DEFAULT | NONE | SHARED | EXCLUSIVE];

-- SQL Server
DROP INDEX [ IF EXISTS ] index_name ON schema.table_name;

SQL DROP INDEX Parameters

index_name (identifier) - Name of the index to drop.
IF EXISTS (keyword) - Skip error if the index does not exist (PostgreSQL, SQL Server 2016+).
CONCURRENTLY (keyword) - Drops index without locking writes but is slower (PostgreSQL).
CASCADE | RESTRICT (keyword) - Control dropping of dependent objects (PostgreSQL).
ON table_name (identifier) - Table owning the index (required in MySQL and SQL Server).
ALGORITHM / LOCK (options) - Fine-tune online drop behavior in MySQL.

Example Queries Using SQL DROP INDEX

-- Safely drop a non-critical index in PostgreSQL
DROP INDEX IF EXISTS idx_orders_created_at;

-- Drop multiple indexes at once
DROP INDEX idx_customer_email, idx_customer_signup_date;

-- Online drop in MySQL to avoid locking writes
DROP INDEX idx_sales_region ON sales ALGORITHM = INPLACE LOCK = NONE;

-- SQL Server example with IF EXISTS
DROP INDEX IF EXISTS idx_inventory_sku ON dbo.inventory;

Expected Output Using SQL DROP INDEX

The specified index or indexes are permanently removed
Disk space is released, and future queries no longer have that access path
Successful execution returns a simple confirmation such as "DROP INDEX" (PostgreSQL) or "Query OK, 0 rows affected" (MySQL)

Use Cases with SQL DROP INDEX

Remove redundant or duplicate indexes created during rapid development
Reclaim disk space consumed by rarely used indexes
Improve write performance by eliminating unnecessary index maintenance
Drop an index before altering its definition or recreating it with different columns or storage parameters
Temporarily disable an index during large bulk inserts or ETL operations to speed up loading

Common Mistakes with SQL DROP INDEX

Forgetting that DROP INDEX is irreversible; you must recreate the index to restore it
Attempting to drop an index that enforces a PRIMARY KEY or UNIQUE constraint instead of dropping the constraint
Omitting the table name in dialects that require it (e.g., MySQL, SQL Server)
Running DROP INDEX without assessing query plans, leading to slower reads
Not using IF EXISTS, causing the statement to fail in deployment pipelines if the index is already gone

First Introduced In

SQL:1999

Frequently Asked Questions

Does DROP INDEX remove a primary key?

No. A primary key is enforced by a UNIQUE constraint. Use ALTER TABLE ... DROP CONSTRAINT to remove it; DROP INDEX will fail.

Can I drop multiple indexes in one statement?

Yes. PostgreSQL and Oracle allow a comma-separated list of index names in a single DROP INDEX statement.

How do I avoid table locks while dropping an index?

In PostgreSQL use DROP INDEX CONCURRENTLY; in MySQL use ALGORITHM = INPLACE LOCK = NONE; in SQL Server use ONLINE = ON when rebuilding rather than dropping.

What permissions are required?

Typically the index owner or a superuser/DBA role can drop an index. In SQL Server, you need ALTER permission on the table or membership in db_ddladmin.