SQL Proficiency Self‑Assessment and Evidence (Technical Screen)

Provide a concise self‑rating and concrete, real‑world examples that demonstrate your SQL proficiency across querying, data modeling, and operations. Tailor your examples to analytical workloads and production safety.

Self‑Rating

Rate your SQL proficiency in:

• Querying (window functions, CTEs, joins, aggregation)
• Data Modeling (normalization, dimensional modeling, slowly changing dimensions)
• Operations (performance tuning, deployment/migrations, observability)

Briefly justify each rating (e.g., years, systems used, scale).

1) Complex Query You Authored

Describe a complex query you wrote that used any of: window functions, CTEs, conditional aggregation, or recursion. Include:

• Business goal and why it mattered
• Data size and platform
• Final query structure (CTEs, windows, aggregations)
• Why you chose this design over alternatives

2) Performance Win You Delivered

Walk through a performance optimization you owned end‑to‑end. Include:

• Baseline runtime and/or compute cost
• Bottleneck diagnosis (EXPLAIN/plan findings)
• Concrete changes (indexes, rewrites, partitioning, statistics)
• Measurable after metrics

3) Safe Deployment You Led

Explain how you shipped a SQL/DDL change safely. Include:

• Code review standards (style, tests, linting)
• Migration plan (expand/backfill/contract, feature flags)
• Rollback strategy
• Data correctness validation (row counts, checksums, invariants)

4) Mentoring and Reviews

Describe how you mentor or review others’ SQL. Include:

• Common anti‑patterns you watch for
• A recent example where your feedback improved reliability or speed