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70 SQL interview problems, from easy to hard. Free for everyone.

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Start hereEasyEmployees and their departments

No. 01joinleft joincoalesce

Easy

0 of 20 solved

  1. Not started. 01Employees and their departmentsjoin · left join · coalesce
  2. Not started. 02Big orders with customer and productjoin · inner join · multi table
  3. Not started. 03Customers who never orderedjoin · anti join · left join
  4. Not started. 04Orders and spend per customerjoin · left join · group by
  5. Not started. 05Delivered and cancelled orders per restaurantgroup by · conditional aggregation · case
  6. Not started. 06Restaurants with a high average ordergroup by · having · avg
  7. Not started. 07Total pay when the bonus can be emptynull · coalesce · case
  8. Not started. 08Rides that cost more than the averagesubquery · scalar subquery · avg
  9. Not started. 09Employees who earn more than their managerjoin · self join · payroll
  10. Not started. 10Find duplicate email addressesgroup by · having · duplicates
  11. Not started. 11Orders and revenue per month in 2026date · strftime · group by
  12. Not started. 12Histogram of order sizeshistogram · group by · integer division
  13. Not started. 13Swap the seats of neighbourscase · modulo · swap
  14. Not started. 14Repeat customer rategroup by · conditional aggregation · percentage
  15. Not started. 15Pairs who follow each otherself join · join · exists
  16. Not started. 16Customers who stopped orderingjoin · group by · having
  17. Not started. 17Order lines whose order is missinganti join · left join · not exists
  18. Not started. 18Sign-ups per email domainstring · substr · instr
  19. Not started. 19Customers who live in Delhistring · like · trim
  20. Not started. 20Active students in each coursemany to many · join table · left join

Medium

0 of 30 solved

  1. Not started. 01Big spendersgroup by · having · aggregate
  2. Not started. 02Top two salaries in each departmentwindow function · dense rank · top n per group
  3. Not started. 03Second highest salarysubquery · distinct · limit offset
  4. Not started. 04Top two dishes of each restaurantwindow function · row number · top n per group
  5. Not started. 05Running total of daily revenuewindow function · running total · sum over
  6. Not started. 06Three day moving average of sign-upswindow function · moving average · avg over
  7. Not started. 07Day over day change in orderswindow function · lag · day over day
  8. Not started. 08First and last order amount of each customerwindow function · first value · last value
  9. Not started. 09Cancellation rate by cityconditional aggregation · case · percentage
  10. Not started. 10Share of revenue by categorywindow function · percent of total · sum over
  11. Not started. 11Pivot: sales per product for each monthpivot · conditional aggregation · case
  12. Not started. 12De-duplicate: keep the latest row per emailwindow function · row number · deduplication
  13. Not started. 13Orders above the average of the same customersubquery · correlated subquery · cte
  14. Not started. 14Drivers with the most completed ridessubquery · group by · having
  15. Not started. 15Month over month revenue growthwindow function · lag · month over month
  16. Not started. 16Best seller of each category in each monthwindow function · rank · top n per group
  17. Not started. 17First paid order after the free trialleft join · join condition · min
  18. Not started. 18Employees who never changed managergroup by · having · count distinct
  19. Not started. 19How many orders are in each status nowwindow function · row number · greatest n per group
  20. Not started. 20End of day balance of each accountwindow function · running total · sum over
  21. Not started. 21Double-booked roomsself join · interval overlap · join
  22. Not started. 22Daily revenue with the empty daysrecursive cte · calendar · left join
  23. Not started. 23Find the missing ticket numbersrecursive cte · anti join · sequence
  24. Not started. 24Employees in each salary bandhistogram · case · range join
  25. Not started. 25Average days between orderswindow function · lag · julianday
  26. Not started. 26Products bought togetherself join · market basket · pairs
  27. Not started. 27Top three products and the rest as Otherstop n · window function · row number
  28. Not started. 28The second order of each customerwindow function · row number · nth per group
  29. Not started. 29Share of users by number of orderscumulative distribution · window function · running total
  30. Not started. 30Duplicate wishlist rows: keep the first, list the restdeduplication · window function · row number

Hard

0 of 20 solved

  1. Not started. 01Longest login streakgaps and islands · window function · row number
  2. Not started. 02Group page views into sessionssessionization · window function · lag
  3. Not started. 03Purchase funnel conversionfunnel · conversion · conditional aggregation
  4. Not started. 04Monthly retention by signup cohortcohort · retention · date
  5. Not started. 05Median delivery fee by citymedian · window function · row number
  6. Not started. 06Everyone who reports to a manager, at any levelrecursive cte · hierarchy · tree
  7. Not started. 07Customers who make the first 80 percent of revenuewindow function · running total · pareto
  8. Not started. 08Rolling 7 day active userscount distinct · correlated subquery · self join
  9. Not started. 09Users active three weeks in a rowgaps and islands · window function · row number
  10. Not started. 10Merge repeated price rows into periodsgaps and islands · window function · lag
  11. Not started. 11P90 latency of each servicepercentile · window function · row number
  12. Not started. 12Year over year revenue by monthself join · left join · cte
  13. Not started. 13Friend suggestions from mutual friendsself join · union · anti join
  14. Not started. 14Fewest flights from Mumbai to every cityrecursive cte · graph · shortest path
  15. Not started. 15Spells of three or more school days absentgaps and islands · window function · row number
  16. Not started. 16Funnel conversion by devicefunnel · conversion · cte
  17. Not started. 17Revenue at the price in force on the order dayas of join · scd · correlated subquery
  18. Not started. 18Days with a sudden traffic spikewindow function · rolling window · range frame
  19. Not started. 19The first move that makes stock negativewindow function · running total · sum over
  20. Not started. 20New versus returning customer revenue by monthcohort · conditional aggregation · count distinct
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