Problems

Filter by difficulty, tag, company, or solved status. Queries run in DuckDB in your browser.

Status	Title	Difficulty	Tags
—	001. Select All Employees	easy	SELECT
—	002. Filter Employees by Salary	easy	SELECT WHERE
—	003. Order Employees by Salary	easy	ORDER BY SELECT
—	004. Count Employees	easy	COUNT aggregate
—	005. Employees With Departments	easy	SELECT INNER JOIN
—	006. Distinct Job Titles	easy	SELECT DISTINCT
—	007. Top 5 Highest-Paid Employees	easy	SELECT ORDER BY LIMIT
—	008. Employees Hired After 2022	easy	SELECT WHERE date functions
—	009. Employees Without a Manager	easy	SELECT WHERE IS NULL
—	010. Total Salary Budget	easy	SELECT SUM aggregate
—	011. Average Product Price	easy	SELECT AVG aggregate
—	012. Most Expensive Product	easy	SELECT MAX aggregate
—	013. Cheapest Product	easy	SELECT MIN aggregate
—	014. Customer Count by Country	easy	SELECT GROUP BY COUNT
—	015. Products Out of Stock	easy	SELECT WHERE
—	016. Employees With No Department	easy	SELECT LEFT JOIN IS NULL
—	017. Salary Tier Label	easy	SELECT CASE
—	018. Customer Name Search	easy	SELECT WHERE LIKE
—	019. Orders in a Price Range	easy	SELECT WHERE BETWEEN
—	020. Customers from Specific Cities	easy	SELECT WHERE IN
—	021. Coalesce Missing Department Name	easy	SELECT COALESCE LEFT JOIN
—	022. Uppercase Product Names	easy	SELECT string functions
—	023. Extract Order Year	easy	SELECT date functions EXTRACT
—	024. Total Orders per Customer	easy	SELECT GROUP BY COUNT
—	025. Count Unique Product Categories	easy	SELECT COUNT DISTINCT
—	026. Orders with Status Pending	easy	SELECT WHERE
—	027. Employees Earning Above 100k	easy	SELECT WHERE
—	028. Sort Products by Price Descending	easy	SELECT ORDER BY
—	029. Paginate Products (Page 3, 5 per page)	easy	SELECT ORDER BY LIMIT
—	030. Monthly Order Count	easy	SELECT GROUP BY date functions
—	031. Average Salary by Department	medium	GROUP BY AVG aggregate
—	032. Rank Employees by Salary	medium	window functions RANK ORDER BY
—	033. Daily Running Revenue	medium	window functions SUM running total
—	034. Departments with 3 or More Employees	medium	GROUP BY HAVING COUNT
—	035. Customers with At Least One Order	medium	SELECT EXISTS subquery
—	036. Customers with No Orders	medium	SELECT EXISTS subquery
—	037. Products Never Ordered	medium	SELECT LEFT JOIN IS NULL
—	038. Employees Earning Above Their Department Average	medium	SELECT correlated subquery AVG
—	039. Manager Names via Self Join	medium	SELECT self join INNER JOIN
—	040. Order Line Details	medium	SELECT INNER JOIN
—	041. Top-Earning Departments (CTE)	medium	SELECT CTE GROUP BY
—	042. Combined List: Employees and Customers Named Alex	medium	SELECT UNION WHERE
—	043. First Order per Customer	medium	SELECT ROW_NUMBER window functions
—	044. Dense Rank Products by Price Within Category	medium	SELECT DENSE_RANK window functions
—	045. Salary Quartiles	medium	SELECT NTILE window functions
—	046. Month-over-Month Revenue Change	medium	SELECT LAG window functions
—	047. Preview Next Month Revenue with LEAD	medium	SELECT LEAD window functions
—	048. All Employees and Departments (Full Outer Join)	medium	SELECT FULL OUTER JOIN
—	049. All Size-Color Combinations (Cross Join)	medium	SELECT CROSS JOIN
—	050. Order Count by Status (Conditional Aggregation)	medium	SELECT CASE conditional aggregation
—	051. Top 3 Products per Category by Price	medium	SELECT ROW_NUMBER window functions
—	052. Find Duplicate Customer Emails	medium	SELECT GROUP BY HAVING
—	053. Revenue Share per Category	medium	SELECT window functions SUM
—	054. Year-over-Year Order Revenue Growth	medium	SELECT LAG CTE
—	055. First Purchase Amount per Customer	medium	SELECT FIRST_VALUE window functions
—	056. Most Recent Order per Customer	medium	SELECT LAST_VALUE window functions
—	057. Employee Tenure in Full Years	medium	SELECT date functions
—	058. Monthly New Customer Signups	medium	SELECT GROUP BY date functions
—	059. Second Highest Salary	medium	SELECT DENSE_RANK window functions
—	060. Employees Sharing the Same Salary	medium	SELECT self join GROUP BY
—	061. Cumulative Revenue Percentage by Department	medium	SELECT window functions SUM
—	062. Products with Above-Average Rating	medium	SELECT subquery AVG
—	063. Count Employees with Missing Salary	medium	SELECT IS NULL COUNT
—	064. Revenue per Unit Sold (Safe Division with NULLIF)	medium	SELECT NULLIF CASE
—	065. Category Revenue Summary (Chained CTEs)	medium	SELECT CTE GROUP BY
—	066. Top-Spending Customers (Derived Table)	medium	SELECT subquery GROUP BY
—	067. Extract Email Domain	medium	SELECT string functions GROUP BY
—	068. Revenue by Category and Order Status	medium	SELECT conditional aggregation CASE
—	069. 7-Day Rolling Active Users	medium	SELECT window functions date functions
—	070. Products with Zero Total Sales	medium	SELECT LEFT JOIN IS NULL
—	071. Rank Departments by Total Payroll	medium	SELECT GROUP BY SUM
—	072. Customer Lifetime Value	medium	SELECT GROUP BY SUM
—	073. Orders from Last Quarter	medium	SELECT WHERE BETWEEN
—	074. Products per Category as Comma-Separated List	medium	SELECT string functions GROUP BY
—	075. Average Days Between Customer Orders	medium	SELECT LAG window functions
—	076. Monthly Order Completion Rate	medium	SELECT conditional aggregation date functions
—	077. Deduplicate Rows with ROW_NUMBER	medium	SELECT ROW_NUMBER window functions
—	078. Customers with High-Value Orders	medium	SELECT IN subquery
—	079. Customer Cohort by First Order Month	medium	SELECT CTE date functions
—	080. 3-Month Moving Average Revenue	medium	SELECT window functions AVG
—	081. Account Running Balance	medium	SELECT window functions SUM
—	082. Retained Customers: Ordered in Both Month 1 and Month 2	medium	SELECT INTERSECT date functions
—	083. Find Gaps in Sequential Order IDs	medium	SELECT gaps and islands window functions
—	084. Custom Sort Priority with CASE in ORDER BY	medium	SELECT CASE ORDER BY
—	085. Employees Who Share the Same Manager	medium	SELECT self join GROUP BY
—	086. All Departments Including Empty Ones	medium	SELECT RIGHT JOIN GROUP BY
—	087. Third Highest Salary	medium	SELECT DENSE_RANK window functions
—	088. Fulfilled Orders Percentage per Month	medium	SELECT conditional aggregation date functions
—	089. Category with the Highest Average Price	medium	SELECT GROUP BY AVG
—	090. Customers Who Ordered Every Month of 2026	medium	SELECT GROUP BY HAVING
—	091. Managers Paid Above Team Average	hard	self join CTE subquery
—	092. Longest Consecutive Login Streak Today	hard	gaps and islands window functions date functions
—	093. Median Salary Without PERCENTILE	hard	SELECT correlated subquery CASE
—	094. Org Chart: All Direct and Indirect Reports	hard	SELECT recursive CTE
—	095. Session Identification from Login Events	hard	SELECT window functions LAG
—	096. Churned vs Retained Customers	hard	SELECT CTE date functions
—	097. Cohort Retention Matrix (Months 0–3)	hard	SELECT CTE conditional aggregation
—	098. Frequently Bought Together (Market Basket)	hard	SELECT self join COUNT
—	099. Running Balance with Overdraft Detection	hard	SELECT window functions SUM
—	100. Employee Hierarchy Depth	hard	SELECT recursive CTE COUNT
—	101. String Length Function	easy	SELECT LENGTH string functions
—	102. UPPER and LOWER String Functions	easy	SELECT UPPER LOWER
—	103. Trim Leading and Trailing Whitespace	easy	SELECT TRIM LTRIM
—	104. Concatenate First and Last Name	easy	SELECT CONCAT string functions
—	105. Extract Category Code from SKU	easy	SELECT SUBSTRING string functions
—	106. Replace Words in Review Text	easy	SELECT REPLACE string functions
—	107. Filter Orders by Date	easy	SELECT WHERE date functions
—	108. Extract Year from Hire Date	easy	SELECT EXTRACT date functions
—	109. Find Orders Placed in September	easy	SELECT EXTRACT date functions
—	110. Calculate Project Duration in Days	easy	SELECT DATEDIFF date functions
—	111. Round Discounted Prices	easy	SELECT ROUND math functions
—	112. Ceiling and Floor of Order Amounts	easy	SELECT CEIL FLOOR
—	113. Find Accounts Far from Target Balance	easy	SELECT ABS WHERE
—	114. Find Products with Quantity Divisible by 3	easy	SELECT MOD WHERE
—	115. Calculate Square Area and Diagonal	easy	SELECT POWER SQRT
—	116. Return First Available Phone Number	easy	SELECT COALESCE NULL handling
—	117. Avoid Division by Zero with NULLIF	easy	SELECT NULLIF NULL handling
—	118. Find Top-Level Employees with No Manager	easy	SELECT WHERE IS NULL
—	119. Find Products with a Description	easy	SELECT WHERE IS NOT NULL
—	120. Filter Employees by Salary Range	easy	SELECT WHERE BETWEEN
—	121. Filter Products by Category Using IN	easy	SELECT WHERE IN
—	122. Exclude Cancelled and Returned Orders	easy	SELECT WHERE NOT IN
—	123. Find Gmail Customers Using LIKE	easy	SELECT WHERE LIKE
—	124. Match Employee Codes with _ Wildcard	easy	SELECT WHERE LIKE
—	125. Find Products NOT Starting with S	easy	SELECT WHERE NOT LIKE
—	126. Filter with Multiple AND Conditions	easy	SELECT WHERE AND
—	127. Filter with Multiple OR Conditions	easy	SELECT WHERE OR
—	128. Mix AND and OR with Parentheses	easy	SELECT WHERE AND
—	129. Total Amount Spent per Customer	easy	SELECT SUM GROUP BY
—	130. Average Rating per Product	easy	SELECT AVG ROUND
—	131. Most Recent Hire Date per Department	easy	SELECT MAX GROUP BY
—	132. First Product Name Alphabetically per Category	easy	SELECT MIN GROUP BY
—	133. COUNT(*) vs COUNT(column)	easy	SELECT COUNT NULL handling
—	134. Count Distinct Customers	easy	SELECT COUNT DISTINCT
—	135. Map Status Codes to Labels with CASE WHEN	easy	SELECT CASE WHEN conditional logic
—	136. Assign Salary Grade with CASE WHEN Ranges	easy	SELECT CASE WHEN conditional logic
—	137. Handle NULL Bonus with CASE WHEN	easy	SELECT CASE WHEN NULL handling
—	138. Sort by Department and Salary	easy	SELECT ORDER BY sorting
—	139. Sort Products by Profit Margin	easy	SELECT ORDER BY arithmetic
—	140. Paginate Results with LIMIT and OFFSET	easy	SELECT LIMIT OFFSET
—	141. Top 5 Orders by Amount Using FETCH FIRST	easy	SELECT FETCH FIRST ORDER BY
—	142. Rename Columns with AS Alias	easy	SELECT AS column alias
—	143. Use Table Aliases in a JOIN	easy	SELECT table alias INNER JOIN
—	144. Calculate Price Including Tax	easy	SELECT arithmetic calculated column
—	145. Join Orders with Customer Details	easy	SELECT INNER JOIN joins
—	146. Find Customers Who Have Never Ordered	easy	SELECT LEFT JOIN IS NULL
—	147. List All Unique Order Statuses	easy	SELECT DISTINCT filtering
—	148. Find Unique Department-City Combinations	easy	SELECT DISTINCT filtering
—	149. Count Orders by Status	easy	SELECT GROUP BY COUNT
—	150. Total Revenue by Department and Quarter	easy	SELECT GROUP BY SUM
—	151. Customers Who Spent More Than $500	easy	SELECT HAVING SUM
—	152. Products Ordered by More Than 2 Customers	easy	SELECT HAVING COUNT
—	153. Group Orders by Month Using DATE_TRUNC	easy	SELECT DATE_TRUNC GROUP BY
—	154. Find Active Subscriptions After a Date	easy	SELECT WHERE CURRENT_DATE
—	155. Pad Invoice Numbers with LPAD	easy	SELECT LPAD RPAD
—	156. Reverse Strings and Detect Palindromes	easy	SELECT REVERSE CASE WHEN
—	157. Find the Position of @ in Email Addresses	easy	SELECT POSITION INSTR
—	158. CHAR_LENGTH vs LENGTH on Messages	easy	SELECT CHAR_LENGTH LENGTH
—	159. Replace NULL Commission with IFNULL	easy	SELECT IFNULL NULL handling
—	160. Find Employees Earning Above Average Salary	easy	SELECT subquery WHERE
—	161. Row Number Within Each Department	medium	window functions ROW_NUMBER PARTITION BY
—	162. Rank Sales Representatives with Ties	medium	window functions RANK ORDER BY
—	163. Game Leaderboard with Dense Rank	medium	window functions DENSE_RANK PARTITION BY
—	164. Month-over-Month Revenue Change Using LAG	medium	window functions LAG ORDER BY
—	165. Time Until Next Customer Event Using LEAD	medium	window functions LEAD PARTITION BY
—	166. Salary Quartile Buckets Using NTILE	medium	window functions NTILE ORDER BY
—	167. Percentile Rank of Exam Scores	medium	window functions PERCENT_RANK ORDER BY
—	168. Cumulative Distribution of Product Prices	medium	window functions CUME_DIST ORDER BY
—	169. Department Max and Min Salary Using FIRST_VALUE and LAST_VALUE	medium	window functions FIRST_VALUE LAST_VALUE
—	170. Running Total of Daily Sales	medium	window functions SUM OVER ORDER BY
—	171. 3-Day Moving Average of Stock Closing Price	medium	window functions AVG OVER ROWS BETWEEN
—	172. Count Orders Per Customer Without GROUP BY	medium	window functions COUNT OVER PARTITION BY
—	173. Compare Each Product Price to Its Category Min and Max	medium	window functions MIN OVER MAX OVER
—	174. Employees Earning Above Their Department Average	medium	correlated subquery SELECT WHERE
—	175. Customers Who Have Placed at Least One Order	medium	EXISTS subquery SELECT
—	176. Products That Have Never Been Ordered	medium	NOT EXISTS subquery SELECT
—	177. Chained CTEs for Layered Sales Analysis	medium	CTE WITH GROUP BY
—	178. Traverse Org Chart Hierarchy with Recursive CTE	medium	recursive CTE WITH RECURSIVE UNION ALL
—	179. Combine Customer Lists with UNION ALL vs UNION	medium	UNION ALL UNION deduplication
—	180. Customers Who Bought Both Online and In-Store	medium	INTERSECT SET operations SELECT
—	181. Products Not Currently on Sale Using EXCEPT	medium	EXCEPT SET operations SELECT
—	182. Pivot Quarterly Sales into Columns Using CASE	medium	PIVOT CASE WHEN GROUP BY
—	183. Unpivot Quarterly Columns to Rows Using UNION ALL	medium	UNPIVOT UNION ALL SELECT
—	184. Comma-Separated Employee List Per Department	medium	STRING_AGG GROUP BY aggregation
—	185. Aggregate Products into an Array Per Category	medium	ARRAY_AGG GROUP BY aggregation
—	186. Extract Fields from a JSON Attributes Column	medium	JSON json_extract_string WHERE
—	187. Filter Users by Email Pattern Using REGEXP	medium	REGEXP SIMILAR TO string functions
—	188. Extract Email Domain Using SPLIT_PART	medium	SPLIT_PART string functions SELECT
—	189. Subscription Expiry and Days Remaining	medium	date arithmetic INTERVAL CURRENT_DATE
—	190. Fill Date Gaps Using GENERATE_SERIES	medium	GENERATE_SERIES LEFT JOIN date functions
—	191. Find Missing IDs in a Sequence	medium	gaps GENERATE_SERIES EXCEPT
—	192. Find Consecutive Activity Streaks (Islands Problem)	medium	islands window functions LAG
—	193. Deduplicate Orders Keeping the Latest Entry	medium	deduplication ROW_NUMBER CTE
—	194. Top 2 Products Per Category by Revenue	medium	TOP N per group ROW_NUMBER CTE
—	195. Each Sale as a Percentage of Total Revenue	medium	window functions SUM OVER percentage
—	196. Count New Customers Acquired Each Month	medium	CTE GROUP BY MIN
—	197. Revenue by Order Status Using CASE Inside SUM	medium	CASE WHEN SUM GROUP BY
—	198. Full Department Salary Statistics in One Query	medium	GROUP BY COUNT SUM
—	199. Show Each Employee with Their Manager's Name	medium	self join LEFT JOIN hierarchy
—	200. Order Details with Customer and Product Names	medium	JOIN three-table join INNER JOIN
—	201. Four-Table JOIN with Category Filter	medium	JOIN four-table join INNER JOIN
—	202. Find Customers Who Have Never Placed an Order	medium	LEFT JOIN NULL check IS NULL
—	203. All Product Color and Size Combinations Using CROSS JOIN	medium	CROSS JOIN Cartesian product SELECT
—	204. Most Recent Order Per Customer Using LATERAL JOIN	medium	LATERAL CROSS JOIN LATERAL correlated subquery
—	205. Weekly Sales Totals Using DATE_TRUNC	medium	DATE_TRUNC GROUP BY SUM
—	206. Year-over-Year Revenue Growth Using LAG	medium	window functions LAG ORDER BY
—	207. Month-over-Month Revenue Growth Rate	medium	window functions LAG ORDER BY
—	208. User Cohort Retention by First Purchase Month	medium	cohort analysis CTE DATE_TRUNC
—	209. Month-2 Retention Rate Calculation	medium	CTE COUNT DISTINCT LEFT JOIN
—	210. Funnel Analysis with Step-by-Step Conversion Rates	medium	CTE LAG COUNT DISTINCT
—	211. ABC Inventory Classification by Cumulative Revenue	medium	CTE window functions SUM OVER
—	212. Customer Tier Segmentation Using NTILE	medium	window functions NTILE ORDER BY
—	213. Revenue Concentration — Cumulative % Per Customer	medium	window functions SUM OVER cumulative
—	214. Median Salary Per Department Using PERCENTILE_CONT	medium	PERCENTILE_CONT WITHIN GROUP ORDER BY
—	215. Find the Most Frequently Occurring Rating (Mode)	medium	GROUP BY COUNT RANK
—	216. Salary Spread by Department Using STDDEV_POP	medium	STDDEV_POP GROUP BY AVG
—	217. Weighted Average Purchase Price Per Product	medium	GROUP BY SUM weighted average
—	218. Rolling 7-Day Revenue Sum	medium	window functions SUM OVER ROWS BETWEEN
—	219. Identify SLA Breaches Using DATEDIFF	medium	DATEDIFF CASE WHEN date arithmetic
—	220. Pivot Monthly Revenue into Jan–Dec Columns	medium	PIVOT CASE WHEN GROUP BY
—	221. Multi-Level Aggregation (Aggregate of Aggregates)	medium	SELECT GROUP BY subquery
—	222. Scalar Subquery in SELECT Clause	medium	SELECT correlated subquery AVG
—	223. Subquery in FROM Clause (Derived Table / Inline View)	medium	SELECT subquery FROM
—	224. Multiple Window Functions in One Query	medium	SELECT window functions ROW_NUMBER
—	225. Running Maximum with RANGE BETWEEN UNBOUNDED PRECEDING	medium	SELECT window functions MAX OVER
—	226. Monthly Session Counts with Date-Based Partition	medium	SELECT window functions COUNT OVER
—	227. Named Window Using the WINDOW Clause	medium	SELECT window functions WINDOW clause
—	228. FILTER Clause with Aggregate Functions	medium	SELECT FILTER GROUP BY
—	229. Conditional COUNT with CASE Expression	medium	SELECT GROUP BY COUNT
—	230. Revenue Share per Category Using Window SUM	medium	SELECT window functions SUM OVER
—	231. Compare Each Employee to Their Department Average Salary	medium	SELECT window functions AVG OVER
—	232. Detect Price Changes Using LAG	medium	SELECT window functions LAG
—	233. Days Until Next Event Using LEAD	medium	SELECT window functions LEAD
—	234. Classify Employees into Salary Bands Using CASE	medium	SELECT CASE GROUP BY
—	235. Employees in Top 10% by Salary Using PERCENT_RANK	medium	SELECT window functions PERCENT_RANK
—	236. Ratio of Each Category to Total Revenue	medium	SELECT GROUP BY SUM
—	237. Rank Products Within Each Brand by Price	medium	SELECT window functions RANK
—	238. First and Last Purchase Date per Customer	medium	SELECT GROUP BY MIN
—	239. Customers Who Never Made a Second Purchase	medium	SELECT GROUP BY HAVING
—	240. Aggregate Orders by Weekday vs Weekend	medium	SELECT EXTRACT ISODOW
—	241. Count Orders by Hour of Day	medium	SELECT EXTRACT HOUR
—	242. Products with High Average Review Rating	medium	SELECT JOIN GROUP BY
—	243. Customers Who Purchased from Every Category	medium	SELECT JOIN GROUP BY
—	244. Email Domain Frequency Analysis	medium	SELECT GROUP BY COUNT
—	245. Phone Number Format Validation with SIMILAR TO	medium	SELECT SIMILAR TO LIKE
—	246. Longest Gap Between Consecutive Orders per Customer	medium	SELECT window functions LAG
—	247. Days Since Last Order per Customer	medium	SELECT GROUP BY MAX
—	248. New vs Returning Customers per Month	medium	SELECT CTE GROUP BY
—	249. Repeat Purchase Rate Calculation	medium	SELECT subquery COUNT
—	250. Customer Purchase Frequency Distribution	medium	SELECT GROUP BY COUNT
—	251. RFM Analysis — Recency, Frequency, Monetary Buckets	medium	SELECT CTE window functions
—	252. Product Co-Purchase Analysis	medium	SELECT self join GROUP BY
—	253. Sales Velocity — Units Sold per Day per Product	medium	SELECT GROUP BY SUM
—	254. Inventory Days Remaining Calculation	medium	SELECT JOIN ROUND
—	255. Supplier Lead Time Analysis	medium	SELECT GROUP BY AVG
—	256. Average Order Value by Acquisition Channel	medium	SELECT GROUP BY AVG
—	257. Revenue per Employee by Department	medium	SELECT JOIN GROUP BY
—	258. Budget vs Actual Spend Comparison	medium	SELECT JOIN COALESCE
—	259. Join on Multiple Columns (Composite Key)	medium	SELECT JOIN composite key
—	260. Finding Duplicate Records Across Columns	medium	SELECT GROUP BY HAVING
—	261. Remove Duplicates Keeping the Most Recent Record	medium	SELECT window functions ROW_NUMBER
—	262. Comparing Two Datasets with FULL OUTER JOIN	medium	SELECT FULL OUTER JOIN COALESCE
—	263. Detecting Anomalies Using Z-Score Approach	medium	SELECT CTE JOIN
—	264. Rolling 30-Day Distinct Customer Count	medium	SELECT self join GROUP BY
—	265. Month-End Date Calculation	medium	SELECT DATE_TRUNC INTERVAL
—	266. Assign Sales to Fiscal Year Quarters	medium	SELECT CASE EXTRACT
—	267. Count Business Days Between Two Dates	medium	SELECT generate_series EXTRACT
—	268. Calculate Age in Years from Birthdate	medium	SELECT AGE EXTRACT
—	269. Timestamp to Date Conversion and Daily Grouping	medium	SELECT DATE_TRUNC CAST
—	270. Detect Overlapping Date Ranges	medium	SELECT self join date ranges
—	271. Assign Row Numbers Within Department Groups	medium	SELECT window functions ROW_NUMBER
—	272. Split Comma-Separated Tags and Count Frequency	medium	SELECT STRING_TO_ARRAY UNNEST
—	273. Aggregating JSON Array Element Counts	medium	SELECT json_array_length JSON
—	274. Finding Maximum Streak of Consecutive Login Days	medium	SELECT CTE ROW_NUMBER
—	275. Customer Segments by Spending Quartile	medium	SELECT CTE window functions
—	276. Product Categories with Month-over-Month Revenue Decline	medium	SELECT CTE window functions
—	277. Employees Promoted in the Last 6 Months	medium	SELECT JOIN WHERE
—	278. Transactions More Than 3 Standard Deviations Above Mean	medium	SELECT subquery AVG
—	279. Cumulative Sum That Resets on Partition Change	medium	SELECT window functions SUM OVER
—	280. Multi-Step CTE Pipeline for Complex Analytics	medium	SELECT CTE JOIN
—	281. Recursive Bill of Materials Explosion	hard	recursive CTE self join aggregation
—	282. Full Org Chart Path as String	hard	recursive CTE string concatenation tree traversal
—	283. Graph Shortest Path via BFS	hard	recursive CTE graph traversal BFS
—	284. Fibonacci Sequence via Recursive CTE	hard	recursive CTE sequence generation BIGINT
—	285. Sliding 30-Day Revenue Window per Customer	hard	window functions RANGE BETWEEN interval arithmetic
—	286. Session Stitching with 30-Minute Gap Tolerance	hard	window functions LAG CTE
—	287. Merge Overlapping Subscription Intervals	hard	window functions CTE islands and gaps
—	288. Time-Series Gap Filling with Zero Revenue Days	hard	GENERATE_SERIES LEFT JOIN CROSS JOIN
—	289. Monthly Sales Pivot Table (Jan–Dec)	hard	pivot CASE aggregation
—	290. Quarterly Revenue Unpivot (Wide to Long Format)	hard	unpivot UNION ALL normalization
—	291. Busiest 3 Consecutive Days by Revenue	hard	window functions ROWS BETWEEN LEAD
—	292. Median Salary by Department using PERCENTILE_CONT	hard	PERCENTILE_CONT ordered-set aggregate window functions
—	293. Fraud Detection: 3+ Transactions Within 1 Hour	hard	self join CTE timestamp arithmetic
—	294. Customer Lifetime Value Projection	hard	CTE aggregation arithmetic
—	295. Cohort Retention Analysis Pipeline	hard	CTE DATE_TRUNC AGE
—	296. Nearest Price Match Across Two Catalogs	hard	CROSS JOIN window functions ROW_NUMBER
—	297. Balanced Task Distribution with NTILE	hard	NTILE window functions CTE
—	298. String Parsing: Extract Structured Data from Concatenated Field	hard	SPLIT_PART string functions data cleaning
—	299. Weighted Composite Product Ranking	hard	window functions CTE normalization
—	300. Maximum Concurrent Bookings per Room	hard	CTE UNION ALL window functions
—	301. Compute Profit per Product	easy	SELECT arithmetic calculated column
—	302. Count Orders by Status	easy	GROUP BY COUNT aggregate
—	303. Find Employees in a Named Department	easy	JOIN INNER JOIN WHERE
—	304. Products Below Reorder Level	easy	SELECT WHERE filtering
—	305. Extract Day of Week from Order Date	easy	SELECT EXTRACT date functions
—	306. Find Customers with No Phone Number	easy	SELECT WHERE IS NULL
—	307. Calculate Salary After a 10% Bonus	easy	SELECT arithmetic calculated column
—	308. Products Whose Name Starts with 'A'	easy	SELECT WHERE LIKE
—	309. Total Revenue per Product	easy	GROUP BY SUM aggregate
—	310. Filter Orders by a Specific Date	easy	SELECT WHERE date functions
—	311. Sort Employees by Hire Date	easy	SELECT ORDER BY sorting
—	312. Count Products per Category	easy	GROUP BY COUNT aggregate
—	313. Find the Highest and Lowest Salary	easy	SELECT MAX MIN
—	314. Customers with Long Names	easy	SELECT WHERE LENGTH
—	315. Uppercase Product Names	easy	SELECT string functions UPPER
—	316. Score Remainder with the Modulo Operator	easy	SELECT arithmetic MOD
—	317. Calculate the Discount Amount per Product	easy	SELECT arithmetic calculated column
—	318. Count Orders Grouped by Year and Month	easy	GROUP BY COUNT EXTRACT
—	319. Orders in a Date Range (BETWEEN)	easy	SELECT WHERE BETWEEN
—	320. Count NULL Values in a Column	easy	SELECT COUNT IS NULL
—	321. Assign Letter Grades with CASE WHEN	easy	SELECT CASE CASE WHEN
—	322. Fetch the First 3 Products Alphabetically (LIMIT)	easy	SELECT ORDER BY LIMIT
—	323. Filter Employees by Status Using IN	easy	SELECT WHERE IN
—	324. Format Order IDs with Zero-Padding	easy	SELECT LPAD string functions
—	325. All Departments Including Those with No Employees	easy	RIGHT JOIN JOIN joins
—	326. Generate All Month–Category Combinations	easy	CROSS JOIN JOIN joins
—	327. Pick the First Non-NULL Name with COALESCE	easy	SELECT COALESCE NULL handling
—	328. High-Volume, High-Value Customers (HAVING with AND)	easy	GROUP BY HAVING COUNT
—	329. Customers Who Have Placed at Least One Order	easy	SELECT EXISTS subquery
—	330. Combine Employees and Contractors with UNION	easy	UNION SET operations SELECT
—	331. Customers With Strictly Increasing Order Values	medium	CTE window functions LAG
—	332. Rank Products by Revenue Within Each Category	medium	CTE window functions RANK
—	333. Monthly Active User Count	medium	DATE_TRUNC COUNT DISTINCT GROUP BY
—	334. Churn Detection: Customers Inactive for 90+ Days	medium	CTE subquery date arithmetic
—	335. Top-Selling Product in Each Region	medium	CTE window functions ROW_NUMBER
—	336. Employee Salary Growth Over Time	medium	window functions LAG PARTITION BY
—	337. Order Items With No Discount Applied	medium	LEFT JOIN IS NULL anti-join
—	338. Total Revenue by Day of Week	medium	EXTRACT GROUP BY SUM
—	339. Detect Same-Direction Price and Quantity Changes	medium	CTE window functions LAG
—	340. Cumulative Order Count per Region	medium	window functions SUM OVER PARTITION BY
—	341. Salary Percentile Rank Within Department	medium	window functions PERCENT_RANK PARTITION BY
—	342. Customer Order Gap Alert (30–60 Days)	medium	CTE date arithmetic BETWEEN
—	343. Products Ordered by Every Customer	medium	subquery GROUP BY HAVING
—	344. Top Salesperson Each Quarter	medium	CTE window functions ROW_NUMBER
—	345. Detect Overdue Invoices and Days Late	medium	CASE WHEN date arithmetic IS NULL
—	346. Average Product Rating (Minimum 5 Reviews Required)	medium	GROUP BY HAVING AVG
—	347. Product Price Range Histogram	medium	CASE WHEN GROUP BY COUNT
—	348. Employee vs Manager Salary Gap	medium	self join self-join JOIN
—	349. Revenue From First-Time vs Repeat Purchases	medium	CTE window functions ROW_NUMBER
—	350. 7-Day Rolling Order Count	medium	window functions SUM OVER ROWS BETWEEN
—	351. Most Popular Product Each Month	medium	CTE window functions ROW_NUMBER
—	352. Customers Who Upgraded Their Loyalty Tier	medium	CTE window functions LAG
—	353. Supplier Performance: Promised vs Actual Delivery Days	medium	JOIN GROUP BY AVG
—	354. Category Market Share of Total Revenue	medium	CTE window functions SUM OVER
—	355. Employees Sharing at Least One Project	medium	self join self-join GROUP BY
—	356. Inventory Turnover Rate per Product	medium	SELECT arithmetic calculated column
—	357. Calculate Net Promoter Score (NPS)	medium	FILTER conditional aggregation COUNT
—	358. Orders Where Every Line Item Is Shipped	medium	GROUP BY HAVING FILTER
—	359. Region × Quarter Revenue Pivot Matrix	medium	conditional aggregation FILTER EXTRACT
—	360. Median Days Between Customer Purchases	medium	CTE window functions LAG
—	361. Product Return Rate as Percentage	medium	GROUP BY FILTER conditional aggregation
—	362. Monthly Revenue With Simple Growth Forecast	medium	window functions LAG analytics
—	363. Employees Assigned to Multiple Departments	medium	GROUP BY HAVING COUNT DISTINCT
—	364. High-Value Order Alert (2× Customer Average)	medium	CTE subquery JOIN
—	365. Month-Over-Month Revenue Trend by Category	medium	window functions LAG PARTITION BY
—	366. Time Between Order Status Transitions	medium	CTE window functions LAG
—	367. Assign Customer Lifetime Value Tiers	medium	CTE CASE WHEN GROUP BY
—	368. Product Co-Purchase Affinity Score	medium	self join self-join GROUP BY
—	369. Manager Span of Control (Direct Reports Count)	medium	self join self-join GROUP BY
—	370. Peak Order Hour per Day	medium	CTE window functions ROW_NUMBER
—	371. Regional Sales Rep Performance with Rank	medium	CTE window functions RANK
—	372. Detect Overstocked Products (3× Average Sales)	medium	SELECT WHERE arithmetic
—	373. Win-Back: Customers Who Returned After 90-Day Dormancy	medium	CTE window functions LAG
—	374. Invoice Aging Bucket Report	medium	CTE CASE WHEN GROUP BY
—	375. Employee Headcount by Salary Band	medium	CASE WHEN GROUP BY COUNT
—	376. Percentage of Orders With Multiple Products	medium	subquery COUNT DISTINCT CASE WHEN
—	377. Average Basket Size per Customer	medium	JOIN GROUP BY COUNT DISTINCT
—	378. Product Revenue Contribution via CTE	medium	CTE percentage arithmetic
—	379. Weekly Signup Cohort Active Users	medium	CTE DATE_TRUNC date grouping
—	380. Top 3 Categories by Order Count	medium	GROUP BY COUNT ORDER BY
—	381. Maximum Non-Overlapping Meetings	hard	recursive CTE ROW_NUMBER CTE
—	382. Three-Day Moving Median Revenue	hard	PERCENTILE_CONT WITHIN GROUP correlated subquery
—	383. Required Skills Missing per Employee	hard	CTE LEFT JOIN anti-join
—	384. Point-in-Time Price from SCD Type 2 History	hard	LEAD window functions PARTITION BY
—	385. Two-Hop Follower Influence Score	hard	CTE JOIN aggregation
—	386. Three-Period Loan Amortization	hard	recursive CTE ROUND arithmetic
—	387. Four-Team Single-Elimination Bracket	hard	CTE CASE WHEN JOIN
—	388. Org-Chart Budget Rollup	hard	recursive CTE hierarchy tree traversal
—	389. First, Last, and Linear Touch Attribution	hard	window functions ROW_NUMBER COUNT OVER
—	390. Weekly Cohort Retention Percentages	hard	CTE DATE_TRUNC COUNT DISTINCT
—	391. Project Critical Path Length	hard	recursive CTE MAX JOIN
—	392. Revenue-Maximizing Price per Product	hard	ROW_NUMBER PARTITION BY arithmetic
—	393. Checkout Funnel Drop-Off Rates	hard	CTE LAG COUNT DISTINCT
—	394. Collaborative Filtering Recommendations for User 1	hard	CTE JOIN aggregation
—	395. Intraday Time-Weighted Average Price	hard	LEAD window functions weighted average
—	396. Exponential Moving Average with Alpha 0.3	hard	recursive CTE ROW_NUMBER ROUND
—	397. Nearest Neighbor by Euclidean Distance	hard	CROSS JOIN ROW_NUMBER SQRT
—	398. Multi-Level Sales Commission	hard	subquery CASE WHEN arithmetic
—	399. Portfolio Mean, Volatility, and 95% VaR	hard	JOIN STDDEV_POP AVG
—	400. Monthly Revenue and New-Customer Dashboard	hard	CTE DATE_TRUNC LAG