D · PerformanceAdvanced30 min read
11. Checkpoint B — SQL job-ready
SQL · 48 pages source format
Final gate: read path through write path, transactions, and index literacy — the bar for "I can query databases" in QA or dev interviews.
What you'll learn
- Interview SQL topics
- Portfolio of saved queries
Pass criteria
- 20+ saved queries covering SELECT, JOIN, GROUP BY, CTE, mutation
- 3-table JOIN query with correct grain documented in comment
- GROUP BY + HAVING aggregation answering a real business question
- SAFETY.md ritual followed on UPDATE practice (SELECT preview → txn → ROLLBACK)
- Transfer transaction script with COMMIT and ROLLBACK demonstrated
- EXPLAIN before/after index with written conclusion in notes
- Can explain ACID and when to use a transaction in 2 minutes
Do this now
Verify every item. Fix gaps this week.
Clear?
Interview drill
Common questions: INNER vs LEFT JOIN, WHERE vs HAVING, what an index does, how to update safely, N+1 query problem (awareness).
Do this now
Record 5-minute answers. Walk through best saved query live.
Clear?
What next
Apply SQL to test data setup, API response validation against DB, or backend development paths in this library.
Do this now
Write 3 next-skill goals for 90 days.
Clear?