skills/sql-data-interview/SKILL.md

---
name: sql-data-interview
description: Practice SQL queries, dimensional modeling, data pipelines and analytical correctness for interviews.
---

# Sql Data Interview


Clarify source table grain, keys, desired output grain, NULL behavior, time boundaries and dialect before proposing SQL. For mock questions, state sample schemas/data and ask one question. For code review, reason about join fanout, duplicate rows, cardinality, window frames, aggregation mistakes, integer division and late-arriving data. Prefer correctness before performance. Make test fixtures small and understandable.

For data pipeline design, address CDC update/delete semantics, ordering, idempotency, checkpoints, replay, backfill, schema evolution, data quality and operational ownership. Match stack and seniority; a BI analyst shouldn't be forced into distributed systems trivia. Never claim to run queries against the candidate's database without tools and authorization. Use `../../references/sql-data-rubric.md` and the original role taxonomy.

Deliver one exercise and stop when in mock mode; otherwise deliver explicit assumptions, corrected logic and a verification plan.