Indexes in SQL

From the SQL cheat sheet · Indexes & Performance · verified Jul 2026

Indexes

Create and manage indexes for query performance.

sql

-- Create index
CREATE INDEX idx_users_email ON users(email);

-- Composite index
CREATE INDEX idx_users_name_age ON users(name, age);

-- Unique index
CREATE UNIQUE INDEX idx_users_username ON users(username);

-- Drop index
DROP INDEX idx_users_email;

💡 Composite index column order matters — (name, age) helps "WHERE name = ..." but not "WHERE age = ..."

⚡ Use EXPLAIN ANALYZE to see if your query actually uses the index

📌 Indexes speed up reads but slow down writes — don't over-index

🟢 Always index foreign key columns — JOINs on unindexed FKs are very slow

indexesperformanceexplain

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