Practice questions

1,004 questions across six tracks. Pick a chapter to see its questions, then solve them in your browser.

Try the SQL playground now (no sign-up needed)

SQL

Query a real Postgres database, from SELECT to window functions.

Introduction 3: How a Database Thinks 6 questions · free
Chapter 4: SELECT: Choosing Columns 8 questions · free
Chapter 5: WHERE: Throwing Away Rows 10 questions · free
Chapter 6: ORDER BY, LIMIT and OFFSET 10 questions · free
Chapter 7: NULL: The Empty Box 8 questions
Chapter 8: CASE WHEN: If/Else Inside a Query 8 questions
Chapter 9: Aggregate Functions 10 questions
Chapter 10: GROUP BY: One Answer Per Group 13 questions
Chapter 11: HAVING: Filtering the Groups 10 questions
Chapter 12: INNER JOIN 12 questions
Chapter 13: LEFT JOIN: Keep Everything On The Left 11 questions
Chapter 14: Joining Three or More Tables 10 questions
Chapter 14B: A Table Joined to Itself 10 questions
Chapter 14C: Other JOINs: RIGHT, FULL, and CROSS 3 questions
Chapter 15: UNION: Stacking Results 7 questions
Chapter 16: Subqueries 9 questions
Chapter 17: EXISTS and Correlated Subqueries 9 questions
Chapter 18: CTEs: Naming Your Steps 10 questions
Chapter 19: Text Functions 9 questions
Chapter 20: Date Functions 9 questions
Chapter 21: Numbers and Type Casting 8 questions
Chapter 22: The Big Idea 9 questions
Chapter 23: ROW_NUMBER, RANK and DENSE_RANK 10 questions
Chapter 24: LAG and LEAD 9 questions
Chapter 24B: FIRST_VALUE, LAST_VALUE, and NTH_VALUE 3 questions
Chapter 25: Running Totals and Frames 9 questions
Chapter 26: Top N Per Group 12 questions
Chapter 27: INSERT, UPDATE, DELETE 10 questions
Chapter 28: Transactions: The Undo Button 6 questions
Chapter 29: Tables, Types and Constraints 8 questions
Chapter 30: Views 8 questions
Chapter 31: Indexes and EXPLAIN 6 questions
Chapter 31B: Roles and Permissions: GRANT and REVOKE 4 questions
Chapter 32: The Order Things Actually Happen 6 questions
Chapter 33: Errors You Will Definitely Hit 6 questions
Chapter 35: Mock Test 10 questions
Chapter 36: Recursive CTEs: Queries That Call Themselves 9 questions
Chapter 37: JSON and JSONB: Documents Inside Rows 8 questions
Chapter 38: Arrays: Many Values in One Cell 8 questions
Chapter 39: generate_series and LATERAL: Rows From Nothing 9 questions
Chapter 40: Pivoting: Turning Rows Into Columns 7 questions
Chapter 41: Full-Text Search: Beyond LIKE 7 questions
Chapter 42: Upserts: INSERT … ON CONFLICT 7 questions
Chapter 43: GROUPING SETS, ROLLUP and CUBE 5 questions
Chapter 44: Materialized Views: Caching a Query 5 questions
Chapter 45: Reading a Query Plan: Indexes That Earn Their Keep 7 questions

Excel & Sheets

Formulas that do the work — lookups, dynamic arrays, LAMBDA.

Chapter 1: Anatomy of a Formula & Cell Locking 2 questions · free
Chapter 2: The IF Function & Boolean Tests 2 questions · free
Chapter 3: Multi-Branch Decision Engines 2 questions · free
Chapter 4: Error Handling & Data Auditing 2 questions
Chapter 5: Conditional Counting 1 questions
Chapter 6: Conditional Sums & Revenue Math 4 questions
Chapter 7: Statistical Conditionals 2 questions
Chapter 8: Multi-Range Matrix Math 3 questions
Chapter 9: VLOOKUP Mastery 4 questions
Chapter 10: Two-Way & Flexible Lookups 2 questions
Chapter 11: The Modern Lookup Standard 5 questions
Chapter 12: Text Cleaning & Standardization 3 questions
Chapter 13: Substring Extraction 3 questions
Chapter 14: Delimiter Splitting & Text Assembly 2 questions
Chapter 15: Date Parts & Construction 4 questions
Chapter 16: Rolling Dates & Month-Ends 2 questions
Chapter 17: Working Days, SLAs & Tenure 2 questions
Chapter 18: Google Sheets QUERY — Core Syntax 3 questions
Chapter 19: Google Sheets QUERY — Grouping & Pivots 1 questions
Chapter 20: Google Sheets ARRAYFORMULA Automation 1 questions
Chapter 21: Cross-Workbook Syncing with IMPORTRANGE 1 questions
Chapter 22: Google Sheets Regular Expressions 2 questions
Chapter 23: Sheets Array Magic 1 questions
Chapter 24: Live Web, Finance & Visuals in Sheets 1 questions
Chapter 25: Dynamic Array Filtering 5 questions
Chapter 26: Distinct Deduplication & Sorting 4 questions
Chapter 27: Sequence Generation & Array Reshaping 2 questions
Chapter 28: Variable-Driven Formulas with LET 3 questions
Chapter 29: Custom Functions with LAMBDA 2 questions
Chapter 30: Advanced Array Helper Lambdas 4 questions
Chapter 31: Financial & Loan Math 6 questions
Chapter 32: Statistical Ranking & Positions 3 questions
Chapter 33: Data Validation, Slicers & Pivot Reporting 13 questions

Power Query

Clean and reshape messy data once, refresh it forever.

Chapter 1: The Power Query Paradigm & ETL Architecture 5 questions · free
Chapter 2: Schema Hygiene & Column Selection 5 questions · free
Chapter 3: Row Filtering, Deduplication & Sorting 5 questions · free
Chapter 4: Data Types & Strict Type Conversion 5 questions
Chapter 5: Text Cleansing & Standardization 5 questions
Chapter 6: Text Splitting, Extraction & Delimiters 5 questions
Chapter 7: Date & Time Intelligence 5 questions
Chapter 8: Numeric Operations, Rounding & Statistics 5 questions
Chapter 9: Conditional Columns & Business Rules 5 questions
Chapter 10: Custom Columns & M Arithmetic 5 questions
Chapter 11: Index Columns & Row Sequences 5 questions
Chapter 12: Group By & Table Aggregations 5 questions
Chapter 13: Appending Queries & Stacking Files 5 questions
Chapter 14: Merging Queries & Relational Joins 5 questions
Chapter 15: Pivoting & Unpivoting Data 5 questions
Chapter 16: Transposing, Filling & Structural Fixes 5 questions
Chapter 17: The M Formula Language Anatomy 5 questions
Chapter 18: Custom M Functions & Reusable Logic 5 questions
Chapter 19: Error Handling & Defensive ETL 5 questions
Chapter 20: Master Power Query & ETL Capstone 5 questions

Python

Start from zero and write real programs — no install needed.

Chapter 1: Hello, Python 7 questions · free
Chapter 2: Variables & Data Types 8 questions · free
Chapter 3: Arithmetic & Mathematical Operations 8 questions · free
Chapter 4: Modern String Formatting & Input 8 questions
Chapter 5: Boolean Truth Testing & Comparisons 8 questions
Chapter 6: Decision Trees with if, elif, and else 8 questions
Chapter 7: Definite Loops with for and range() 8 questions
Chapter 8: Indefinite Loops with while & Loop Control 8 questions
Chapter 9: Lists & Mutable Methods 8 questions
Chapter 10: List Comprehensions & Inline Filtering 8 questions
Chapter 11: Dictionaries & Key-Value Lookups 8 questions
Chapter 12: Tuples, Sets & Deduplication 8 questions
Chapter 13: Defining Functions & Return Values 8 questions
Chapter 14: Advanced Functions, Scope & Arguments 8 questions
Chapter 15: Defensive Error Handling with try / except 8 questions
Chapter 16: The Python Standard Library & Projects 8 questions
Chapter 17: NumPy Arrays & Vectorization 8 questions
Chapter 18: Array Filtering & Conditional Logic (np.where & np.select) 8 questions
Chapter 19: Series & DataFrame Anatomy 8 questions
Chapter 20: Precise Indexing & Boolean Masking (.loc vs .iloc) 8 questions
Chapter 21: Data Hygiene & Missing Values 8 questions
Chapter 22: Column Operations, Math & Type Casting 8 questions
Chapter 23: Text Surgery & Regex with .str Accessor 8 questions
Chapter 24: Datetime Intelligence with .dt Accessor 8 questions
Chapter 25: GroupBy Aggregations & Named Multi-Metric Reports 8 questions
Chapter 26: Window Calculations & Group Transforms 8 questions
Chapter 27: Reshaping Data: Pivot Tables & Melting 8 questions
Chapter 28: Relational Joins & Stacking 8 questions
Chapter 29: Business Visualizations with Matplotlib 8 questions
Chapter 30: Statistical Charts with Seaborn 8 questions
Chapter 31: Exploratory Data Analysis (EDA) Workflow 8 questions
Chapter 32: Capstone Business Analytics Case Study 8 questions

DAX

Write DAX measures on a real data model — the formula language of Power BI.

Chapter 1: The Star Schema & Filter Flow 4 questions · free
Chapter 2: Core Aggregations & Safe Math 4 questions · free
Chapter 3: Calculated Columns vs Measures 4 questions · free
Chapter 4: Navigating Relationships with RELATED 4 questions
Chapter 5: The SUMX Iterator 4 questions
Chapter 6: Statistical Iterators: AVERAGEX, MINX & MAXX 3 questions
Chapter 7: Table Filtering with FILTER 3 questions
Chapter 8: Dimension Iteration with VALUES 3 questions
Chapter 9: CALCULATE & Boolean Overwrites 4 questions
Chapter 10: Multi-Condition Filtering & The IN Operator 3 questions
Chapter 11: Preserving Filters with KEEPFILTERS 3 questions
Chapter 12: Removing Filters: ALL & REMOVEFILTERS 5 questions
Chapter 13: Selective Removal with ALLEXCEPT & ALLSELECTED 3 questions
Chapter 14: Calendar Foundations & Date Requirements 3 questions
Chapter 15: Cumulative Metrics: TOTALYTD, TOTALQTD & TOTALMTD 4 questions
Chapter 16: Period Comparisons: Prior Year & YoY Growth 3 questions
Chapter 17: Sequential Shifts & Moving Windows 3 questions
Chapter 18: Variables for Performance & Clean Code 3 questions
Chapter 19: Dynamic Logic, Slicers & Ranking 5 questions
Chapter 20: Context Transition, Secondary Relationships & Capstone 6 questions

Tableau

Calculated fields, level of detail and table calculations: the thinking behind a Tableau view.

Chapter 1: Meet Tableau and the data 5 questions · free
Chapter 2: Multi-dimensional views and granularity 5 questions · free
Chapter 3: Sifting data with filters 5 questions · free
Chapter 4: The Marks card and visual encodings 5 questions
Chapter 5: Arithmetic and profitability formulas 5 questions
Chapter 6: Logical branching with IF and CASE 5 questions
Chapter 7: String cleaning and text normalization 5 questions
Chapter 8: Dates, durations and business calendars 5 questions
Chapter 9: The aggregation boundary and core aggregates 5 questions
Chapter 10: Conditional aggregations and target ratios 5 questions
Chapter 11: The FIXED Level of Detail expression 5 questions
Chapter 12: Advanced FIXED and nested cohorts 5 questions
Chapter 13: Level of detail with INCLUDE and EXCLUDE 5 questions
Chapter 14: Running totals and cumulative trajectories 5 questions
Chapter 15: Ranking, distributions and table filters 5 questions
Chapter 16: Secondary table calculations and ratios 5 questions
Chapter 17: Moving windows and time series lookups 5 questions
Chapter 18: Table calculation direction and addressing 5 questions
Chapter 19: Tableau order of operations and context filters 5 questions
Chapter 20: Master Business Intelligence Capstone 5 questions