Practice
Short, focused questions for every topic — Basic, Intermediate and Advanced. You write every line; hints point the way without giving code. Solve a question to earn XP.
Short, focused questions for every topic — Basic, Intermediate and Advanced. You write every line; hints point the way without giving code. Solve a question to earn XP.
From CREATE TABLE and constraints to window functions and interview combos.
0 / 400 solved
The patterns interviewers ask again and again, collected from every topic.
Design tables with the right columns and types.
PRIMARY KEY, NOT NULL, UNIQUE, CHECK, DEFAULT and FOREIGN KEY.
Add, change and remove rows safely.
Change table structure and save queries as views.
Pick columns and filter rows with conditions.
Sort, take the top rows and remove duplicates.
COUNT, SUM, AVG, MIN, MAX — overall and per group.
Filter groups after aggregating.
INNER, LEFT, RIGHT and FULL joins across tables.
Join a table to itself and build combinations.
Queries inside queries: IN, EXISTS and scalar subqueries.
Break problems into readable steps.
Conditional logic, buckets and pivots.
IS NULL, COALESCE, NULLIF and NULLs in aggregates.
Clean and transform text.
Extract parts, truncate, add and subtract dates.
ROW_NUMBER, RANK, DENSE_RANK, NTILE.
Compare rows and accumulate values.
Combine and compare result sets.
Combine everything — the questions interviews love.
Strings, lists, dicts, loops, lambdas and comprehensions, then NumPy and pandas.
0 / 280 solved
The patterns interviewers ask again and again, collected from every topic.
Slicing, methods, formatting and text puzzles.
Indexing, slicing, sorting and list methods.
Immutable sequences and set operations.
Counting, grouping and looking things up.
Iterate, accumulate, enumerate and zip.
Loop until a condition changes.
Parameters, defaults, return values and recursion.
Small functions and functional tools.
List, dict and set comprehensions.
Arrays, vectorised maths and statistics.
Select columns, filter rows, sort and add columns.
Summaries per group.
Join DataFrames and change their shape.
Missing values, duplicates, text and dates.