recommendedintermediate

SQL for QA Engineers: T-SQL in Everyday Testing

A working course in T-SQL for QA engineers in professional services firms who already know the basics — SELECT, WHERE, a simple JOIN — and now need SQL as a daily testing instrument rather than as a topic. Everything is set in ENGAGE, the fictional engagement and billing platform of Aldervane Advisory LLP: clients, engagements, staff, timesheets, approvals, invoices, an audit log and a migration staging table. One schema, carried through every unit, so the examples are the ones you actually meet — a report total that disagrees with the raw rows, a record the UI claims it saved, a migration that quietly dropped a hundred time entries, a duplicate that only appears under a business key. Each construct is introduced the same way: the problem that makes you reach for it, the construct itself, and the price it charges. LEFT JOIN buys you the missing rows and charges you row multiplication. NOLOCK buys you speed on a shared environment and charges you dirty reads. A green test that never asked the right question costs more than a red one. Nineteen core units cover reading an unfamiliar schema, staying safe on a shared test environment, NULL and three-valued logic, data types and collation, dates and time zones, joins and orphan records, set operations as reconciliation, aggregation, subqueries, CTEs, window functions, test data setup and idempotent teardown, verifying what the application wrote, reading someone else's views and triggers, and turning a SQL check into a deterministic assertion. Five optional units add a local sandbox script, execution plans, client data and AI assistants, an end-to-end migration reconciliation checklist, and normalisation as an explanation of why the schema looks the way it does. Units are open in any order: come for the whole course, or come for the one thing that is biting you today. Scope note: the course teaches you to write queries and to read them. Practice covers both; the certification exam checks reading, recognition and knowledge of constructs, since a written query cannot be machine-verified here.