🗄 Interview Prep

SQL & Databases

Joins, GROUP BY, subqueries, CTEs and window functions, run on real tables in your browser. Asked for back-end, data and full-stack roles.

📘 Learn it from scratch

Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.

Tables & SELECT QueriesFiltering Rows with WHERESorting, Limiting & DISTINCTCounting & Summarizing (Aggregates)Grouping Results with GROUP BYCombining Tables with JOINSubqueries & CTEsINSERT, UPDATE & DELETEDesigning & Creating Tables

100 questions, most asked first

Ordered so the most useful questions for learning each pattern come first.

Any difficulty Easy Medium Hard

All patterns Subqueries Window functions Joins Group by Self joins & CTEs Changing data Dates & strings CASE & NULL Sorting & limits Aggregates Filtering Basics Indexes & transactions Schema design

#3Customers Who Never OrderedJoinsEasyFree #5Find Duplicate EmailsGroup byEasyFree #6Employees Earning More Than Their ManagersSelf joins & CTEsEasyFree #7Average Salary by DepartmentGroup byEasyFree #9INNER vs LEFT vs RIGHT vs FULL JOINJoinsEasyFree #10WHERE vs HAVINGGroup byEasyFree Unlock 33 more SQL & Databases questions · all 1,200 questions for $39/year (about 11¢ a day)See full access #13Number of Orders per Customer (Including Zero)JoinsEasy🔒#16Monthly RevenueDates & stringsEasy🔒#18Products Never OrderedSubqueriesEasy🔒#22Employees Hired in a Date RangeDates & stringsEasy🔒#23Handling NULLs with COALESCECASE & NULLEasy🔒#24Salary Bands with CASECASE & NULLEasy🔒#26Top Customer by Total SpendSorting & limitsEasy🔒#28Each Customer's First Order DateAggregatesEasy🔒#30Daily Active UsersAggregatesEasy🔒#31Who Referred the Most Customers?Self joins & CTEsEasy🔒#33Departments With No EmployeesJoinsEasy🔒#34Employees Without a DepartmentFilteringEasy🔒#35UNION vs UNION ALLBasicsEasy🔒#40Primary keys and foreign keysSchema designEasy🔒#45COUNT(*) vs COUNT(column) vs COUNT(DISTINCT)AggregatesEasy🔒#46DISTINCT vs GROUP BYGroup byEasy🔒#49Extract email domainsDates & stringsEasy🔒#52The Most Popular ProductAggregatesEasy🔒#55Average Order Value by CityAggregatesEasy🔒#57DELETE vs TRUNCATE vs DROPChanging dataEasy🔒#61What is a view?Schema designEasy🔒#72Customers Who Never CancelledGroup byEasy🔒#73City With the Most CustomersGroup byEasy🔒#74Orders Above the Average AmountSubqueriesEasy🔒#76Units Sold per Product (Including Zero)JoinsEasy🔒#77Hires per YearDates & stringsEasy🔒#79Same-Day Duplicate EventsGroup byEasy🔒#83Soft deletesSchema designEasy🔒#87Searching text with LIKEFilteringEasy🔒#88Filtering with IN and BETWEENFilteringEasy🔒#93Every Combination with CROSS JOINJoinsEasy🔒#97Copy Rows with INSERT … SELECTChanging dataEasy🔒#100How to approach any SQL interview questionBasicsEasy🔒