SQL Study Plans for Interview Prep
Practise one skill at a time. Each plan picks up to 20 questions from the SQLQuokka library and orders them from easy to hard, so you build up from the basics before the harder interview patterns. Every question runs in your browser in MySQL or PostgreSQL.
SQL Basics
Every SQL interview starts here. These questions cover choosing rows with WHERE, combining conditions, handling NULLs, sorting with ORDER BY and keeping only the rows you need with LIMIT and DISTINCT.
SQL Joins
Joins are where most interview answers go wrong: rows disappear, duplicate or turn NULL. Work through inner and outer joins, self joins on the same table and anti joins that find rows with no match.
GROUP BY & Aggregation
Most analytics questions boil down to grouping rows and summarising them. Practise COUNT, SUM and AVG, filtering groups with HAVING, counting distinct values and building ratios with conditional aggregation.
Subqueries & CTEs
Harder questions need more than one step. Learn to break a problem into stages with WITH clauses, compare rows against a group result with correlated subqueries and reuse derived tables.
Window Functions
Window functions are the most common topic in mid-level and senior SQL interviews. Rank rows within groups, compare each row with the previous one and compute running totals without collapsing your result.
Dates & Time
Product and analytics interviews love dates. Practise date arithmetic, grouping by month, comparing periods, finding consecutive days and building retention and cohort reports.
Hard Questions
Ready for senior-level rounds? These questions combine several techniques at once: window functions inside CTEs, gaps and islands, sessionization and multi-step funnel and retention analysis.