SQL Joins Practice Problems

Joins combine rows from two or more tables on a matching key - INNER JOIN keeps only matches, LEFT JOIN keeps every row from the left side and fills the right with NULLs. Nearly every SQL screen leans on them, from a simple two-table lookup to three-table chains and the classic LEFT JOIN + IS NULL anti-join ("customers who never ordered"). If you only drill one topic before an interview, make it this one.

23 problems across 4 schemas · 3 free for registered users. Each runs your query in an isolated SQLite sandbox with instant, graded feedback.