LEETCODE Crack SQL Interview in 50 Qs

A fully–documented collection of solutions to the LeetCode SQL-50 problems. The goal isn’t just to get the right answer, but to explain the reasoning.

Why this repository?

“It is a strange situation where in order to understand something, I must be able to teach it to others, and I’ve found this really works for me. ” — Duncan McArdle

Feel free to PR an alternative approach to any of the questions.

What’s inside each solution file?

Problem Statement: A concise restatement of the task (including the relevant table schema).
Approach : A step-by-step outline of the thought process.
SQL Solution : The final query.

Name		Name	Last commit message	Last commit date
.gitattributes		.gitattributes
Article Views I.sql		Article Views I.sql
Average Selling Price.sql		Average Selling Price.sql
Average Time of Process per Machine.sql		Average Time of Process per Machine.sql
Big Countries.sql		Big Countries.sql
Biggest Single Number.sql		Biggest Single Number.sql
Classes With at Least 5 Students.sql		Classes With at Least 5 Students.sql
Confirmation Rate.sql		Confirmation Rate.sql
Consecutive Numbers.sql		Consecutive Numbers.sql
Count Salary Categories.sql		Count Salary Categories.sql
Customer Who Visited but Did Not Make Any Transactions.sql		Customer Who Visited but Did Not Make Any Transactions.sql
Customers Who Bought All Products.sql		Customers Who Bought All Products.sql
Delete Duplicate Emails.sql		Delete Duplicate Emails.sql
Department Top Three Salaries.sql		Department Top Three Salaries.sql
Employee Bonus.sql		Employee Bonus.sql
Employees Whose Manager Left the Company.sql		Employees Whose Manager Left the Company.sql
Exchange Seats.sql		Exchange Seats.sql
Find Customer Referee.sql		Find Customer Referee.sql
Find Followers Count.sql		Find Followers Count.sql
Find Users With Valid E-Mails.sql		Find Users With Valid E-Mails.sql
Fix Names in a Table.sql		Fix Names in a Table.sql
Friend Requests II Who Has the Most Friends.sql		Friend Requests II Who Has the Most Friends.sql
Game Play Analysis IV.sql		Game Play Analysis IV.sql
Group Sold Products By The Date.sql		Group Sold Products By The Date.sql
Immediate Food Delivery II.sql		Immediate Food Delivery II.sql
Invalid Tweets.sql		Invalid Tweets.sql
Investments in 2016.sql		Investments in 2016.sql
Last Person to Fit in the Bus.sql		Last Person to Fit in the Bus.sql
List the Products Ordered in a Period.sql		List the Products Ordered in a Period.sql
Managers with at Least 5 Direct Reports.sql		Managers with at Least 5 Direct Reports.sql
Monthly Transactions I.sql		Monthly Transactions I.sql
Movie Rating.sql		Movie Rating.sql
Not Boring Movies.sql		Not Boring Movies.sql
Number of Unique Subjects Taught by Each Teacher.sql		Number of Unique Subjects Taught by Each Teacher.sql
Patients With a Conditions.sql		Patients With a Conditions.sql
Percentage of Users Attended a Contest.sql		Percentage of Users Attended a Contest.sql
Primary Department for Each Employee.sql		Primary Department for Each Employee.sql
Product Price at a Given Date.sql		Product Price at a Given Date.sql
Product Sales Analysis I.sql		Product Sales Analysis I.sql
Product Sales Analysis III.sql		Product Sales Analysis III.sql
Project Employees I.sql		Project Employees I.sql
Queries Quality and Percentage.sql		Queries Quality and Percentage.sql
README.md		README.md
Recyclable and Low Fat Products.sql		Recyclable and Low Fat Products.sql
Replace Employee ID With The Unique Identifier.sql		Replace Employee ID With The Unique Identifier.sql
Restaurant Growth.sql		Restaurant Growth.sql
Rising Temperature.sql		Rising Temperature.sql
Second Highest Salary.sql		Second Highest Salary.sql
Students and Examinations.sql		Students and Examinations.sql
The Number of Employees Which Report to Each Employee.sql		The Number of Employees Which Report to Each Employee.sql
Triangle Judgement.sql		Triangle Judgement.sql
User Activity for the Past 30 Days I.sql		User Activity for the Past 30 Days I.sql

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