What is the N+1 problem in GraphQL and how do you solve it?

The N+1 problem occurs when resolving a list of items causes a database query for each item, leading to severe performance degradation.

If you query 100 users, and their posts resolver fetches posts by user ID, you make 1 query for users, and 100 queries for posts (1+100). The solution is to use the DataLoader pattern, which batches and caches requests, turning the 100 queries into a single SELECT * FROM posts WHERE user_id IN (...).