A complete SQL interview prep portal, organised from basics to advanced. Every answer comes with a diagram and runnable SQL so you can explain the idea and show the code.
The fundamentals every SQL interview starts with: SELECT, WHERE, JOINs, keys, GROUP BY, NULL handling and the core clauses.
BeginnerSubqueries, aggregate vs window functions, HAVING vs WHERE, set operators, CTEs and the differences interviewers love to probe.
IntermediateWindow function depth, recursive CTEs, isolation levels, execution plans, pivoting and the questions that separate seniors.
AdvancedWrite-the-query challenges: find duplicates, second highest salary, running totals, gaps and islands, top N per group.
AppliedModeling relationships, choosing keys and data types, ER diagrams, one-to-many vs many-to-many, and schema trade-offs.
DesignIndexing strategy, index seek vs scan, reading execution plans, why a query is slow, sargable predicates and tuning.
AdvancedProcedures vs functions, parameters and output, error handling with TRY CATCH, transactions, and when to use each.
IntermediateThe normal forms explained: 1NF, 2NF, 3NF and BCNF, functional dependencies, anomalies, and when to denormalize.
DesignWork through the categories above, sharpen your query writing with the hands-on SQL exercises, then go deeper with the SQL interview guide and the SQL functions library. For focused help, book a session with a mentor.