N+1 problem

Learn the N+1 query trap.

N+1 problem

The N+1 problem is one query returning N rows, then a separate query per row. It is slow.

-- YANLIŞ: her sipariş için ayrı müşteri sorgusu
-- DOĞRU: JOIN ile tek sorgu
SELECT o.id, c.name FROM orders o JOIN customers c ON o.customer_id = c.id;

JOIN solves N+1.

o.id, c.name is selected from orders o. customers c is joined on o.customer_id = c.id, keeping only matching rows.

N+1 problem — details

The N+1 problem is common in ORMs. It is solved with JOIN or eager loading.

For example, listing 100 orders and fetching each customer with a separate query means 101 queries; a single JOIN returns the same data in one query.

Exercise N+1 problem

Solve the N+1 problem with JOIN: combine orders and customers in one query.

Show example solution

SELECT o.id, c.name FROM orders o JOIN customers c ON o.customer_id = c.id;

Test yourself

Add JOIN

SELECT o.id, c.name FROM orders o ____ customers c ON o.customer_id = c.id

Show answer

SELECT o.id, c.name FROM orders o JOIN customers c ON o.customer_id = c.id

N+1 problem: match the terms

N+1

many queries
JOIN

single query
slow

problem
ORM

common
What solves the N+1 problem?
- JOIN
- DISTINCT
- INDEX
- VIEW
Show answer

JOIN — JOIN solves N+1.

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