Learning level
Easy
SQL Essentials
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.
Joins & Relationship Reasoning
Join types, grain, cardinality, duplicate explosions, and the habit of proving why rows multiplied.
Aggregation & Business Metrics
Grouped metrics, HAVING filters, distinct counts, conditional aggregation, and trustworthy metric definitions.
Learning level
Medium
CTEs, Subqueries & Query Structure
Layered query design, debuggable intermediate results, and SQL that is easy to narrate in interviews.
Window Functions & Analytics Patterns
Ranking, offsets, running totals, deduplication, retention, cohorts, and event sequence analysis.
Time, Events & Semi-Structured Data
Timestamp logic, time zones, event tables, JSON, arrays, late data, and ordering tradeoffs.
Learning level
Advanced
Data Engineering SQL Usage
Incremental loads, MERGE patterns, upserts, slowly changing dimensions, snapshots, and backfills.
Data Quality, Debugging & Auditing
Duplicate checks, null checks, referential tests, reconciliation, anomaly queries, and audit evidence.
Warehouse Performance & Cost
Partitions, clustering, pruning, query plans, scan cost, and warehouse-aware optimization habits.
SQL Interview Playbook
Clarifying assumptions, narrating query logic, debugging live, and explaining senior-level tradeoffs.