🗄 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.

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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

Ranked by how often each question comes up in real interviews. #1 is the most common.

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🔒