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SQLProfessionalabout 8 hours18 lessons
Recommended first: Schema Studio
Schema Studio taught you to design a safe database. Counting House is where that database has to survive a busy Monday. You are the data engineer for Fernhollow Co-op Market, a community marketplace where members top up wallets, buy from growers and bakers, and sellers get paid out. Each lesson adds one production habit to a single SQL file: a double-entry ledger that refuses to go out of balance, payouts that survive client retries, a transactional outbox, a job queue with leases and dead letters, an audit trail, tenant isolation, indexes you can prove, and reports that close the month. By the end the console shows the books balancing.
Each lesson adds one working part to your build.
Chapter 1
A double-entry ledger that cannot be unbalanced: tables, bulk posting, guard triggers and integer money.
Chapter 2
Retried requests, reliable events, leased jobs and an audit trail: failure-proofing in SQL.
Chapter 3
What to delete, what to keep, how tenants stay apart, and how to prove a query is fast.
Chapter 4
Running balances, incremental summaries, roll-ups that survive late data, and checks that the books match reality.
Chapter 5
Change a live ledger without stopping it, then close the month and prove the books balance.