The N+1 Query Problem
Why 20 posts become 21 queries, and how to fix it with a join
What you'll learn
- Why a query inside a loop is slow
- How ORMs hide extra queries
- Fixing it with a JOIN or WHERE id IN
- Eager loading, and spotting N+1 in your logs
In this video, we'll look at why a page showing 20 blog posts can end up running 21 database queries. We'll cover what the N+1 query problem is, why running a query inside a loop adds up, and how ORMs hide it from you.
We'll also cover fixing it with a SQL join, batching with WHERE id IN, and eager loading in ORMs like Prisma and Rails.
By the end, you'll know how to spot N+1 queries in your query logs and how to fix them.
