Database LeetCode Problems: All 249,
With Python Solutions

Every problem in this library that LeetCode tags Database. 33 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

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Easy: 100
Medium: 105
Hard: 44

Database problems by difficulty

Showing the first 200 of 249 problems. Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (86)

Easy problems
No.	Problem	Topics
0175	Combine Two Tables	Database
0181	Employees Earning More Than Their Managers	Database
0182	Duplicate Emails	Database
0183	Customers Who Never Order	Database
0196	Delete Duplicate Emails	Database
0197	Rising Temperature	Database
0511	Game Play Analysis I	Database
0577	Employee Bonus	Database
0584	Find Customer Referee	Database
0586	Customer Placing the Largest Number of Orders	Database
0595	Big Countries	Database
0596	Classes With at Least 5 Students	Database
0607	Sales Person	Database
0610	Triangle Judgement	Database
0619	Biggest Single Number	Database
0620	Not Boring Movies	Database
0627	Swap Sex of Employees	Database
1050	Actors and Directors Who Cooperated At Least Three Times	Database
1068	Product Sales Analysis I	Database
0512	Game Play Analysis IIPremium	Database
0597	Friend Requests I: Overall Acceptance RatePremium	Database
0603	Consecutive Available SeatsPremium	Database
0613	Shortest Distance in a LinePremium	Database
1069	Product Sales Analysis IIPremium	Database
1075	Project Employees I	Database
1076	Project Employees IIPremium	Database
1082	Sales Analysis IPremium	Database
1083	Sales Analysis IIPremium	Database
1084	Sales Analysis III	Database
1113	Reported PostsPremium	Database
1141	User Activity for the Past 30 Days I	Database
1142	User Activity for the Past 30 Days IIPremium	Database
1148	Article Views I	Database
1173	Immediate Food Delivery IPremium	Database
1179	Reformat Department Table	Database
1211	Queries Quality and Percentage	Database
1241	Number of Comments per PostPremium	Database
1251	Average Selling Price	Database
1280	Students and Examinations	Database
1294	Weather Type in Each CountryPremium	Database
1303	Find the Team SizePremium	Database
1322	Ads PerformancePremium	Database
1327	List the Products Ordered in a Period	Database
1350	Students With Invalid DepartmentsPremium	Database
1378	Replace Employee ID With The Unique Identifier	Database
1407	Top Travellers	Database
1421	NPV QueriesPremium	Database
1435	Create a Session Bar ChartPremium	Database
1484	Group Sold Products By The Date	Database
1495	Friendly Movies Streamed Last MonthPremium	Database
1511	Customer Order FrequencyPremium	Database
1517	Find Users With Valid E-Mails	Database
1527	Patients With a Condition	Database
1543	Fix Product Name FormatPremium	Database
1565	Unique Orders and Customers Per MonthPremium	Database
1571	Warehouse ManagerPremium	Database
1581	Customer Who Visited but Did Not Make Any Transactions	Database
1587	Bank Account Summary II	Database
1607	Sellers With No SalesPremium	Database
1623	All Valid Triplets That Can Represent a CountryPremium	Database
1633	Percentage of Users Attended a Contest	Database
1661	Average Time of Process per Machine	Database
1667	Fix Names in a Table	Database
1677	Product's Worth Over InvoicesPremium	Database
1683	Invalid Tweets	Database
1693	Daily Leads and Partners	Database
1729	Find Followers Count	Database
1731	The Number of Employees Which Report to Each Employee	Database
1741	Find Total Time Spent by Each Employee	Database
1757	Recyclable and Low Fat Products	Database
1777	Product's Price for Each StorePremium	Database
1789	Primary Department for Each Employee	Database
1795	Rearrange Products Table	Database
1809	Ad-Free SessionsPremium	Database
1821	Find Customers With Positive Revenue this YearPremium	Database
1853	Convert Date FormatPremium	Database
1873	Calculate Special Bonus	Database
1890	The Latest Login in 2020	Database
1939	Users That Actively Request Confirmation MessagesPremium	Database
1965	Employees With Missing Information	Database
1978	Employees Whose Manager Left the Company	Database
2026	Low-Quality ProblemsPremium	Database
2072	The Winner UniversityPremium	Database
2082	The Number of Rich CustomersPremium	Database
2205	The Number of Users That Are Eligible for DiscountPremium	Database
2230	The Users That Are Eligible for DiscountPremium	Database

Medium (82)

Medium problems
No.	Problem	Topics
0176	Second Highest Salary	Database
0177	Nth Highest Salary	Database
0178	Rank Scores	Database
0180	Consecutive Numbers	Database
0184	Department Highest Salary	Database
0550	Game Play Analysis IV	Database
0570	Managers with at Least 5 Direct Reports	Database
0585	Investments in 2016	Database
0602	Friend Requests II: Who Has the Most Friends	Database
0608	Tree Node	Database
0626	Exchange Seats	Database
0534	Game Play Analysis IIIPremium	Database
0574	Winning CandidatePremium	Database
0578	Get Highest Answer Rate QuestionPremium	Database
0580	Count Student Number in DepartmentsPremium	Database
0612	Shortest Distance in a PlanePremium	Database
0614	Second Degree FollowerPremium	Database
1045	Customers Who Bought All Products	Database
1070	Product Sales Analysis III	Database
1077	Project Employees IIIPremium	Database
1098	Unpopular BooksPremium	Database
1107	New Users Daily CountPremium	Database
1112	Highest Grade For Each StudentPremium	Database
1126	Active BusinessesPremium	Database
1132	Reported Posts IIPremium	Database
1149	Article Views IIPremium	Database
1158	Market Analysis I	Database
1164	Product Price at a Given Date	Database
1174	Immediate Food Delivery II	Database
1193	Monthly Transactions I	Database
1204	Last Person to Fit in the Bus	Database
1205	Monthly Transactions IIPremium	Database
1212	Team Scores in Football TournamentPremium	Database
1264	Page RecommendationsPremium	Database
1270	All People Report to the Given ManagerPremium	Database
1285	Find the Start and End Number of Continuous RangesPremium	Database
1308	Running Total for Different GendersPremium	Database
1321	Restaurant Growth	Database
1341	Movie Rating	Database
1355	Activity ParticipantsPremium	Database
1364	Number of Trusted Contacts of a CustomerPremium	Database
1393	Capital Gain/Loss	Database
1398	Customers Who Bought Products A and B but Not CPremium	Database
1440	Evaluate Boolean ExpressionPremium	Database
1445	Apples & OrangesPremium	Database
1454	Active UsersPremium	Database
1459	Rectangles AreaPremium	Database
1468	Calculate SalariesPremium	Database
1501	Countries You Can Safely Invest InPremium	Database
1532	The Most Recent Three OrdersPremium	Database
1549	The Most Recent Orders for Each ProductPremium	Database
1555	Bank Account SummaryPremium	Database
1596	The Most Frequently Ordered Products for Each CustomerPremium	Database
1613	Find the Missing IDsPremium	Database
1699	Number of Calls Between Two PersonsPremium	Database
1709	Biggest Window Between VisitsPremium	Database
1715	Count Apples and OrangesPremium	Database
1747	Leetflex Banned AccountsPremium	Database
1783	Grand Slam TitlesPremium	Database
1811	Find Interview CandidatesPremium	Database
1831	Maximum Transaction Each DayPremium	Database
1841	League StatisticsPremium	Database
1843	Suspicious Bank AccountsPremium	Database
1867	Orders With Maximum Quantity Above AveragePremium	Database
1875	Group Employees of the Same SalaryPremium	Database
1907	Count Salary Categories	Database
1934	Confirmation Rate	Database
1949	Strong FriendshipPremium	Database
1951	All the Pairs With the Maximum Number of Common FollowersPremium	Database
1988	Find Cutoff Score for Each SchoolPremium	Database
1990	Count the Number of ExperimentsPremium	Database
2020	Number of Accounts That Did Not StreamPremium	Database
2041	Accepted Candidates From the InterviewsPremium	Database
2051	The Category of Each Member in the StorePremium	Database
2066	Account BalancePremium	Database
2084	Drop Type 1 Orders for Customers With Type 0 OrdersPremium	Database
2112	The Airport With the Most TrafficPremium	Database
2142	The Number of Passengers in Each Bus IPremium	Database
2159	Order Two Columns IndependentlyPremium	Database
2175	The Change in Global RankingsPremium	Database
2228	Users With Two Purchases Within Seven DaysPremium	Database
2238	Number of Times a Driver Was a PassengerPremium	Database

Hard (32)

Hard problems
No.	Problem	Topics
0185	Department Top Three Salaries	Database
0262	Trips and Users	Database
0601	Human Traffic of Stadium	Database
0569	Median Employee SalaryPremium	Database
0571	Find Median Given Frequency of NumbersPremium	Database
0579	Find Cumulative Salary of an EmployeePremium	Database
0615	Average Salary: Departments VS CompanyPremium	Database
0618	Students Report By GeographyPremium	Database
1097	Game Play Analysis VPremium	Database
1127	User Purchase PlatformPremium	Database
1159	Market Analysis IIPremium	Database
1194	Tournament WinnersPremium	Database
1225	Report Contiguous DatesPremium	Database
1336	Number of Transactions per VisitPremium	Database
1369	Get the Second Most Recent ActivityPremium	Database
1384	Total Sales Amount by YearPremium	Database
1412	Find the Quiet Students in All ExamsPremium	Database
1479	Sales by Day of the WeekPremium	Database
1635	Hopper Company Queries IPremium	Database
1645	Hopper Company Queries IIPremium	Database
1651	Hopper Company Queries IIIPremium	Database
1767	Find the Subtasks That Did Not ExecutePremium	Database
1892	Page Recommendations IIPremium	Database
1917	Leetcodify Friends RecommendationsPremium	Database
1919	Leetcodify Similar FriendsPremium	Database
1972	First and Last Call On the Same DayPremium	Database
2004	The Number of Seniors and Juniors to Join the CompanyPremium	Database
2010	The Number of Seniors and Juniors to Join the Company IIPremium	Database
2118	Build the EquationPremium	Database
2153	The Number of Passengers in Each Bus IIPremium	Database
2173	Longest Winning StreakPremium	Database
2199	Finding the Topic of Each PostPremium	Database

Eyes only

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 Terra

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python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

Primary display

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Database problems by difficulty

Easy (86)86

Medium (82)82

Hard (32)32

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Easy (86)

Medium (82)

Hard (32)