SQL practice and query-plan lab
Run real SQLite queries on a fresh sample database, inspect joins and compare an indexed query plan.
customers(id, name) has Ada, Lin and Sam. orders(id, customer_id, amount) includes a refund, a zero order and an unassigned order. Each run starts from the same fresh database.
SQLite runs in an isolated browser worker with a three-second execution guard. There is no hard browser memory limit. The first run downloads the runtime; no account or database connection is required. A query plan explains access choices, not measured execution time.
Turn the result into understanding
Start with customer totals. Explain why Sam needs a zero even though there is no matching order. Then inspect the lookup plan with and without the index. The tiny sample teaches query semantics; use representative data to assess production performance.
Reference: Official documentation