N+1 queries 🗃️ SQL

Performance: N+1 query problem (one query per row in a loop)

Code runs one query to load a list, then one more query per item — hundreds of queries per page.

Seen on: SQL

Meaning

Not an error message, but the most common cause of slow pages and connection pool exhaustion with ORMs. Lazy-loaded relations accessed in a loop trigger a query each time.

Common causes

  • Lazy relations accessed in loops/templates
  • Missing eager loading (include/with/select_related/JOIN FETCH)

⚡ Quick fix

  1. Eager-load relations (Laravel with(), Django select_related/prefetch_related, Rails includes, EF Include)
  2. Log query counts per request in development

Detailed fix by platform

SQL

  1. SELECT o.*, u.email FROM orders o JOIN users u ON u.id = o.user_id WHERE o.status = 'paid';

How to diagnose

  1. Count — Queries per request?
  2. Pattern — Same query repeated with different ids?

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