SQL for Data + Engineering Interviews
From window functions to query plans — interview-grade SQL.
Practice the SQL questions data engineers, analysts, and backend engineers actually face — window functions, CTEs, query-plan reasoning, dimensional modeling. Every problem runs against a real Postgres instance, not a paper exercise.
Free to start · Pro at $9.99/mo unlocks live-SQL mock interviews
Who this track is for
- Aspiring data analysts / engineers prepping for product-company loops.
- Backend engineers tired of being SQL-shaky in design reviews.
- Anyone who's been told 'just learn window functions' and given no syllabus.
Why Coachingle for SQL
What separates us from the problem-banks + recorded courses.
Real Postgres, not pseudo-SQL
Every problem runs against a managed Postgres instance with realistic-shape data. You get the actual error message, not "Wrong answer".
Query plan literacy
Most SQL prep stops at "writes a query that works". We teach EXPLAIN, index choice, hash joins, and when to denormalize.
Pattern-keyed flashcards
Top-N per group, gap-detection, running totals, hierarchical queries — each pattern is a flashcard you spaced-repeat against.
Mock loops for analyst + DE roles
Take-home + onsite-style live SQL with our AI interviewer. Scorecard tracks query correctness, performance reasoning, and clarification-asking.
What you'll cover
Concept coverage drilled across cheatsheets, flashcards, quizzes, and mock interviews.
- ✓Window functions (RANK, DENSE_RANK, LAG/LEAD, NTILE)
- ✓CTEs + recursive queries
- ✓Hash vs merge vs nested-loop joins
- ✓EXPLAIN ANALYZE — reading + acting on plans
- ✓Index choice: B-tree, hash, GIN, partial
- ✓Star vs snowflake schema; slowly-changing dimensions
- ✓Time-series patterns (gap detection, sessionization)
- ✓Aggregation tricks (FILTER, GROUPING SETS, ROLLUP)
Frequently asked questions
Which dialect — Postgres, MySQL, BigQuery?
Postgres-first because it's the cleanest superset of standard SQL. We flag dialect-specific syntax (e.g. BigQuery STRUCT, Snowflake QUALIFY) where they differ. 95% of interview SQL is dialect-portable.
Is this for analysts or engineers?
Both. We split tracks into 'Analyst' (heavy on window functions, dashboarding patterns) and 'Engineer' (query plans, index design, denormalization tradeoffs). You can switch tracks anytime.
Do I need Pro?
Free tier covers all 70+ patterns + flashcards. Pro lifts the daily tutor quota + unlocks the AI mock interview with scorecard PDF.
Ready to drill SQL?
Free to start. No credit card. Pro at $9.99/mo unlocks the AI mock interview.