Topic overview
Learn selection, filtering, joins, grouping, windows, CTEs, subqueries, date logic, and query interpretation.
Core concepts
Think in relations: keys, grain, cardinality, null behavior, join types, aggregation levels, and execution cost.
Why it matters
Data roles depend on SQL for analysis, debugging, pipeline validation, reporting, and product decision support.
Interview relevance
Most data interviews use SQL to test correctness, communication, edge cases, and whether you understand the data shape.