Database Indexing Traps That Slow You Down

Indexes are lifesavers for query performance. But many devs fall into indexing traps that do the opposite.

Trap #1: Too Many Indexes

Every index speeds reads but slows writes. Adding indexes blindly can choke inserts.

Trap #2: Wrong Column Order

Multi-column indexes must match the query order.

SQL
-- Index on (last_name, first_name)
-- Query must filter last_name first
SELECT * FROM users WHERE last_name = 'Doe' AND first_name = 'John';
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Trap #3: Forgetting Covering Indexes Queries fetching small sets of columns can benefit from covering indexes.

SQL
CREATE INDEX idx_user_email ON users(email);
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Quick Checklist

✅ Index columns used in WHERE and JOIN.

✅ Avoid indexing every column.

✅ Monitor slow queries regularly.

What To Do Next

Run EXPLAIN on slow queries. Index based on evidence, not guesses.