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 ThresholdFree 2Accounts Flagged for ReviewFree 3Vehicles Outside the Mileage BandFree 4Streams in the Launch MarketsFree 5Rides Missing a RatingFree 6Devices Still on Old Firmware 7Advertisers Active on Launch Day 8Podcasts Worth Featuring 9Below Reorder Level 10Flagged or High-Value, No Test Accounts

Grouping and aggregation0 / 1212

11Cities With Enough Driver Supply 12One-Video Channels 13Revenue per Customer 14Ticket Volume per Channel 15Depot Stock Extremes 16Average Watch Minutes per Show 17Pick Errors by Warehouse and Shift 18Sellers Above the Payout Floor 19Categories Above the Overall Average 20Products with Broad Appeal 21Big-Spending Customers 22Single-Category Customers

Joining tables0 / 1414

23Tickets with the Requester's Name 24Students Without Any Enrollment 25Refunds with Customer Emails 26Reps Out-Earning Their Team Leads 27Orders Shipped from Their Own Region 28Listings and Their Review Counts 29Hometown Rides 30Tracks Nobody Saved 31App Review Queue by Category 32Managers Out-Earned by a Report 33Order Line Totals 34Employees, Unassigned Included 35Review Details 36Mutual Follows★

Subqueries, CTEs and Set Operations0 / 55

37Plans Priced Above the Average 38Shoppers Seen in Both Channels 39SKUs Listed but Never Scanned 40Top Bid in Every Auction 41Customers Whose Latest Order Was Refunded★

Sorting and Pagination0 / 1010

42Five Priciest Listings 43Third Page of Newest Products 44Three Lowest Scores 45Second Page of Search Results 46Best Effective Price per Item 47Stable Leaderboard Cutoff 48Support Queue in Triage Order 49Feed Page After a Cursor 50How Many Result Pages 51Second Page, Two per Page

Strings and Text0 / 1414

52Masked Card Endings 53Signups by Email Domain 54Normalized Brand Counts 55SKU Prefix Audit 56Shipping Label Lines 57Handles That Break the Rules 58Signups by Area Code 59Split Full Names for the Badge Printer 60Initials from a Full Name 61How Many Tags per Post 62Title to URL Slug 63Names Starting with a Vowel 64Letters Without Spaces 65Alerts Carrying a SEV1 Code

Numbers and Dates0 / 1313

66Attachment Sizes in Whole Megabytes 67Which Quarter Each Sale Falls In 68Hour of Each Event 69Whole Dollars and Loose Cents 70Days from Order to Delivery 71Quotes per Month 72Rate Change Percent, in Basis Points 73Minutes from Page to Acknowledge 74Renewals Due This Quarter 75Weekend vs Weekday Orders 76Tenure in Days 77Round Cents to the Nearest Dollar 78Discount Percentage

Duplicates, Median and Mode0 / 55

79Duplicate Contact Emails 80First Signup per Email 81Most Common Complaint Category 82Repeated Transactions 83Median Delivery Minutes per Carrier★

Ranges and Gaps0 / 1313

84Break in the Invoice Sequence 85Double-Booked Meeting Rooms 86Three Failed Checks in a Row 87Coverage Lapses Between Policies 88Lowest Free Short Code 89Deliveries Active at the Noon Cutover 90Peak Simultaneous Streams per Account★91Free Gift-Card Number Ranges★92Double-Booked Rooms★93Longest Run of Consecutive Numbers★94How Many Separate Streaks★95Smallest Missing Positive★96Three Busy Days in a Row★

Window Functions I: Ranking and Top-N0 / 1717

97Number the Leaderboard 98Revenue Rank Within Category 99Top Two Spenders per Region 100Gap to the Department Ceiling 101Podium Places with Shared Medals 102Top Earner in Every Department, Ties Kept 103Second-Fastest Lap per Kart 104Where the Tiebreak Actually Mattered 105Global Top Three, Ties Included 106Second-Highest Salary per Department 107Top Two Products per Category 108Competition Ranking with Gaps 109Flag the Top Earner in Each Department 110Cheapest Product per Category 111Podium Medals by Rank 112Runner-Up Bid, or Nothing 113Median Resolution Hours per Team★

Window Functions II: Running Values0 / 1616

114Warmer Than the Day Before 115Running Account Balance 116Day-over-Day Signup Change 117Three-Day Moving Unit Total 118Share of Category Revenue 119Drawdown from the Running Peak 120Days Until the Next Order 121Sensor Drift Since First Reading 122Readings That Repeat the Previous One 123Flag Each Customer's First Order 124Days Since the Previous Order 125Running Count Within Category 126Difference from the Category Baseline 127Cumulative Signups 128Last Rider Under the Weight Limit 129Longest Daily Usage Streak★

Reporting and Reshaping0 / 1414

130Label Each Order's Size 131Web vs Store Revenue by Region 132Order Size Buckets 133Quarterly Columns to Rows 134Category Spend with a Total Row 135Signup Grid: Plans Across, Regions Down 136Device Specs from Attribute Rows 137Regional Revenue with Zero-Filled Blanks 138Checkout Funnel Drop-Off 139Pass and Fail Counts per Exam 140Score Spread per Team 141Rating Buckets per Product 142Unpivot Subject Scores 143Average Sale Price, Unsold Included

Hierarchical and Recursive Queries0 / 1414

144Weekly Signup Cohorts, Quiet Weeks Included 145Ancestors of Category 7 146Total Budget Under the CEO 147Root, Inner, or Leaf 148Everyone Under the Director★149Escalation Depth per Employee★150Folder Sizes Including Subfolders★151Sales Calendar with Zero Days★152Approval Chain to the Top★153Total Screws in the Speaker Build★154Category Breadcrumbs★155Pages Reachable from Home★156Missing Ticket Numbers★157Total Reports per Manager★

Product Analytics Patterns0 / 1515

158Signup Activation Rate 159Click-Through Rate by Campaign 160Monthly Active Users 161Power Users 162Repeat Purchase Rate 163View-to-Buy Conversion Rate 164Churned After June 165New Users per Day 166Session Bounce Rate 167Confirmed on the Second Day, Not the First★168Seven-Day Signup Retention by Cohort★169Pages Your Friends Like★170Bad-Experience Rate in the First 14 Days★171Returned the Very Next Day★172Cancellation Rate for Trusted Users★