Learning level
Read a table and its grain, shape a query, select and filter deliberately, handle types and NULLs, count safely, and inspect results like an engineer.
Join types, grain, cardinality, duplicate explosions, and the habit of proving why rows multiplied.
Grouped metrics, HAVING filters, distinct counts, conditional aggregation, and trustworthy metric definitions.
Learning level
Layered query design, debuggable intermediate results, and SQL that is easy to narrate in interviews.
Ranking, offsets, running totals, deduplication, retention, cohorts, and event sequence analysis.
Timestamp logic, time zones, event tables, JSON, arrays, late data, and ordering tradeoffs.
Learning level
Incremental loads, MERGE patterns, upserts, slowly changing dimensions, snapshots, and backfills.
Duplicate checks, null checks, referential tests, reconciliation, anomaly queries, and audit evidence.
Partitions, clustering, pruning, query plans, scan cost, and warehouse-aware optimization habits.
Clarifying assumptions, narrating query logic, debugging live, and explaining senior-level tradeoffs.