SQL & Data

Problems

172 SQL problems in 14 stages, from filtering rows through joins and window functions to product analytics patterns. Each query is checked against real results.

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SQL & Data problems

Filtering rows0 / 1010

1Shipped Orders Above a ThresholdFreeEasy 2Accounts Flagged for ReviewFreeEasy 3Vehicles Outside the Mileage BandFreeEasy 4Streams in the Launch MarketsFreeEasy 5Rides Missing a RatingFreeEasy 6Devices Still on Old FirmwareEasy 7Advertisers Active on Launch DayEasy 8Podcasts Worth FeaturingMedium 9Below Reorder LevelMedium 10Flagged or High-Value, No Test AccountsMedium

Grouping and aggregation0 / 1212

11Cities With Enough Driver SupplyFreeEasy 12One-Video ChannelsFreeEasy 13Revenue per CustomerFreeMedium 14Ticket Volume per ChannelFreeMedium 15Depot Stock ExtremesFreeMedium 16Average Watch Minutes per ShowMedium 17Pick Errors by Warehouse and ShiftMedium 18Sellers Above the Payout FloorMedium 19Categories Above the Overall AverageMedium 20Products with Broad AppealMedium 21Big-Spending CustomersMedium 22Single-Category CustomersMedium

Joining tables0 / 1414

23Tickets with the Requester's NameFreeEasy 24Students Without Any EnrollmentFreeMedium 25Refunds with Customer EmailsFreeMedium 26Reps Out-Earning Their Team LeadsFreeMedium 27Orders Shipped from Their Own RegionFreeMedium 28Listings and Their Review CountsMedium 29Hometown RidesMedium 30Tracks Nobody SavedMedium 31App Review Queue by CategoryMedium 32Managers Out-Earned by a ReportMedium 33Order Line TotalsMedium 34Employees, Unassigned IncludedMedium 35Review DetailsMedium 36Mutual FollowsHard

Subqueries, CTEs and Set Operations0 / 55

37Plans Priced Above the AverageEasy 38Shoppers Seen in Both ChannelsEasy 39SKUs Listed but Never ScannedMedium 40Top Bid in Every AuctionMedium 41Customers Whose Latest Order Was RefundedHard

Sorting and Pagination0 / 1010

42Five Priciest ListingsEasy 43Third Page of Newest ProductsEasy 44Three Lowest ScoresEasy 45Second Page of Search ResultsMedium 46Best Effective Price per ItemMedium 47Stable Leaderboard CutoffMedium 48Support Queue in Triage OrderMedium 49Feed Page After a CursorMedium 50How Many Result PagesMedium 51Second Page, Two per PageMedium

Strings and Text0 / 1414

52Masked Card EndingsEasy 53Signups by Email DomainMedium 54Normalized Brand CountsMedium 55SKU Prefix AuditMedium 56Shipping Label LinesMedium 57Handles That Break the RulesMedium 58Signups by Area CodeMedium 59Split Full Names for the Badge PrinterMedium 60Initials from a Full NameMedium 61How Many Tags per PostMedium 62Title to URL SlugMedium 63Names Starting with a VowelMedium 64Letters Without SpacesMedium 65Alerts Carrying a SEV1 CodeMedium

Numbers and Dates0 / 1313

66Attachment Sizes in Whole MegabytesEasy 67Which Quarter Each Sale Falls InEasy 68Hour of Each EventEasy 69Whole Dollars and Loose CentsMedium 70Days from Order to DeliveryMedium 71Quotes per MonthMedium 72Rate Change Percent, in Basis PointsMedium 73Minutes from Page to AcknowledgeMedium 74Renewals Due This QuarterMedium 75Weekend vs Weekday OrdersMedium 76Tenure in DaysMedium 77Round Cents to the Nearest DollarMedium 78Discount PercentageMedium

Duplicates, Median and Mode0 / 55

79Duplicate Contact EmailsEasy 80First Signup per EmailMedium 81Most Common Complaint CategoryMedium 82Repeated TransactionsMedium 83Median Delivery Minutes per CarrierHard

Ranges and Gaps0 / 1313

84Break in the Invoice SequenceMedium 85Double-Booked Meeting RoomsMedium 86Three Failed Checks in a RowMedium 87Coverage Lapses Between PoliciesMedium 88Lowest Free Short CodeMedium 89Deliveries Active at the Noon CutoverMedium 90Peak Simultaneous Streams per AccountHard 91Free Gift-Card Number RangesHard 92Double-Booked RoomsHard 93Longest Run of Consecutive NumbersHard 94How Many Separate StreaksHard 95Smallest Missing PositiveHard 96Three Busy Days in a RowHard

Window Functions I: Ranking and Top-N0 / 1717

97Number the LeaderboardEasy 98Revenue Rank Within CategoryMedium 99Top Two Spenders per RegionMedium 100Gap to the Department CeilingMedium 101Podium Places with Shared MedalsMedium 102Top Earner in Every Department, Ties KeptMedium 103Second-Fastest Lap per KartMedium 104Where the Tiebreak Actually MatteredMedium 105Global Top Three, Ties IncludedMedium 106Second-Highest Salary per DepartmentMedium 107Top Two Products per CategoryMedium 108Competition Ranking with GapsMedium 109Flag the Top Earner in Each DepartmentMedium 110Cheapest Product per CategoryMedium 111Podium Medals by RankMedium 112Runner-Up Bid, or NothingMedium 113Median Resolution Hours per TeamHard

Window Functions II: Running Values0 / 1616

114Warmer Than the Day BeforeEasy 115Running Account BalanceMedium 116Day-over-Day Signup ChangeMedium 117Three-Day Moving Unit TotalMedium 118Share of Category RevenueMedium 119Drawdown from the Running PeakMedium 120Days Until the Next OrderMedium 121Sensor Drift Since First ReadingMedium 122Readings That Repeat the Previous OneMedium 123Flag Each Customer's First OrderMedium 124Days Since the Previous OrderMedium 125Running Count Within CategoryMedium 126Difference from the Category BaselineMedium 127Cumulative SignupsMedium 128Last Rider Under the Weight LimitMedium 129Longest Daily Usage StreakHard

Reporting and Reshaping0 / 1414

130Label Each Order's SizeEasy 131Web vs Store Revenue by RegionMedium 132Order Size BucketsMedium 133Quarterly Columns to RowsMedium 134Category Spend with a Total RowMedium 135Signup Grid: Plans Across, Regions DownMedium 136Device Specs from Attribute RowsMedium 137Regional Revenue with Zero-Filled BlanksMedium 138Checkout Funnel Drop-OffMedium 139Pass and Fail Counts per ExamMedium 140Score Spread per TeamMedium 141Rating Buckets per ProductMedium 142Unpivot Subject ScoresMedium 143Average Sale Price, Unsold IncludedMedium

Hierarchical and Recursive Queries0 / 1414

144Weekly Signup Cohorts, Quiet Weeks IncludedMedium 145Ancestors of Category 7Medium 146Total Budget Under the CEOMedium 147Root, Inner, or LeafMedium 148Everyone Under the DirectorHard 149Escalation Depth per EmployeeHard 150Folder Sizes Including SubfoldersHard 151Sales Calendar with Zero DaysHard 152Approval Chain to the TopHard 153Total Screws in the Speaker BuildHard 154Category BreadcrumbsHard 155Pages Reachable from HomeHard 156Missing Ticket NumbersHard 157Total Reports per ManagerHard

Product Analytics Patterns0 / 1515

158Signup Activation RateMedium 159Click-Through Rate by CampaignMedium 160Monthly Active UsersMedium 161Power UsersMedium 162Repeat Purchase RateMedium 163View-to-Buy Conversion RateMedium 164Churned After JuneMedium 165New Users per DayMedium 166Session Bounce RateMedium 167Confirmed on the Second Day, Not the FirstHard 168Seven-Day Signup Retention by CohortHard 169Pages Your Friends LikeHard 170Bad-Experience Rate in the First 14 DaysHard 171Returned the Very Next DayHard 172Cancellation Rate for Trusted UsersHard