Tracks
The same problems, grouped by topic so you can practice joins before window functions.
Foundations
SELECT, filter, sort, and limit — the queries every interview starts with.
89 problems
SELECT
WHERE
ORDER BY
Aggregates
GROUP BY, HAVING, and summary functions.
116 problems
aggregate
COUNT
SUM
Joins
Combine rows across tables, including self-joins.
37 problems
INNER JOIN
LEFT JOIN
RIGHT JOIN
Subqueries and CTEs
Nested queries, EXISTS, and WITH clauses — including recursive CTEs.
83 problems
subquery
correlated subquery
CTE
Window functions
RANK, LAG, running totals, and top-N per group.
85 problems
window functions
ROW_NUMBER
RANK
NULLs and CASE
Missing values, COALESCE, and conditional labels.
37 problems
IS NULL
COALESCE
NULLIF
Strings and dates
LIKE, EXTRACT, and everyday text/date helpers.
64 problems
string functions
date functions
EXTRACT
Set operations
UNION, INTERSECT, and EXCEPT.
8 problems
UNION
INTERSECT
EXCEPT
Interview patterns
Gaps and islands, duplicates, and other classics.
5 problems
gaps and islands
duplicate detection
top N per group