Mechanical Data Analyst

  Hello All, We are back with another SQL problem, focusing on use case of SQL CASE statement. CASE statement works similar to that of IF - ELSE ladder in other programming languages. This problem requires use of CONCAT() function. You can visit following learning resources related to this particular question : 1. SQL CASE statement -  SQL CASE Statement (w3schools.com) 2. concat function -  CONCAT (Transact-SQL) - SQL Server | Microsoft Docs   The problem below is sourced from HackerRank. You can visit the link:  Binary Tree Nodes | HackerRank Give a try to solve below problem. Solution is provided as usual. Feel free to comment if any queries and also suggest alternate approach to solve this problem. Have a Happy Learning !   You are given a table,  BST , containing two columns:  N  and  P,  where  N  represents the value of a node in  Binary Tree , and  P  is the parent of  N . Write a query to ...

 SQL Leetcode Question No.  177 .  Nth Highest Salary Hello All, We are back with another SQL problem to gain understanding about SQL. This blog-post focuses on SQL user defined function. To know more about SQL user defined function, I highly recommend this blog-post. Learn SQL: User-Defined Functions (sqlshack.com) Give a try to solve below problem. Solution is provided as usual. Feel free to comment if any queries and also suggest alternate approach to solve this problem. Have a Happy Learning !   SQL Schema Table:  Employee +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | salary | int | +-------------+------+ id is the primary key column for this table. Each row of this table contains information about the salary of an employee.   Write an SQL query to report the  n th  highest salary from the  Employee  table. If there is no  n th  highest salary, the query should repo...

Leetcode Problem No. 178  Hello All, We are back with another SQL problem to gain understanding about SQL. This blog-post focuses on SQL window functions, understanding difference between 2 SQL functions RANK() and DENSE_RANK(). Give a try to solve below problem. Solution is provided as usual. Feel free to comment if any queries and also suggest alternate approach to solve this problem. Have a Happy Learning !   178 .  Rank Scores SQL Schema Table:  Scores +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | score | decimal | +-------------+---------+ id is the primary key for this table. Each row of this table contains the score of a game. Score is a floating point value with two decimal places.   Write an SQL query to rank the scores. The ranking should be calculated according to the following rules: The scores should be ranked from the highest to the lowest. If there is a tie between two scores, ...

180 .  Consecutive Numbers   Hello All, I am back with another SQL leetcode solution. This time we are going one step ahead and practice question with medium difficulty. SQL Schema Table:  Logs +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | num | varchar | +-------------+---------+ id is the primary key for this table. id is an autoincrement column.   Write an SQL query to find all numbers that appear at least three times consecutively. Return the result table in  any order . The query result format is in the following example.   Example 1: Input: Logs table: +----+-----+ | id | num | +----+-----+ | 1 | 1 | | 2 | 1 | | 3 | 1 | | 4 | 2 | | 5 | 1 | | 6 | 2 | | 7 | 2 | +----+-----+ Output: +-----------------+ | ConsecutiveNums | +-----------------+ | 1 | +-----------------+ Explanation: 1 is the only number that appears consecutively for at least three ti...

Leetcode question no. 181   181 .  Employees Earning More Than Their Managers SQL Schema Table:  Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key column for this table. Each row of this table indicates the ID of an employee, their name, salary, and the ID of their manager.   Write an SQL query to find the employees who earn more than their managers. Return the result table in  any order . The query result format is in the following example.   Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: ...

  182 .  Duplicate Emails SQL Schema Table:  Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key column for this table. Each row of this table contains an email. The emails will not contain uppercase letters.   Write an SQL query to report all the duplicate emails. Return the result table in  any order . The query result format is in the following example.   Example 1: Input: Person table: +----+---------+ | id | email | +----+---------+ | 1 | a@b.com | | 2 | c@d.com | | 3 | a@b.com | +----+---------+ Output: +---------+ | Email | +---------+ | a@b.com | +---------+ Explanation: a@b.com is repeated two times. Solution : # Write your MySQL query statement below select Email from Person group by Email having count(Email) > 1; Approach : First Approach is finding out count of each email address 1) # Write your MySQ...

Answer to SQL Leetcode Question 183 183 .  Customers Who Never Order   SQL Schema Table:  Customers +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | +-------------+---------+ id is the primary key column for this table. Each row of this table indicates the ID and name of a customer.   Table:  Orders +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | customerId | int | +-------------+------+ id is the primary key column for this table. customerId is a foreign key of the ID from the Customers table. Each row of this table indicates the ID of an order and the ID of the customer who ordered it.   Write an SQL query to report all customers who never order anything. Return the result table in  any order . The query result format is in the following example.   Example 1: Input: Customers table: +----+-------+ | id | name | +---...

Answer to SQL Leetcode question 1757  1757 .  Recyclable and Low Fat Products SQL Schema Table:  Products +-------------+---------+ | Column Name | Type | +-------------+---------+ | product_id | int | | low_fats | enum | | recyclable | enum | +-------------+---------+ product_id is the primary key for this table. low_fats is an ENUM of type ('Y', 'N') where 'Y' means this product is low fat and 'N' means it is not. recyclable is an ENUM of types ('Y', 'N') where 'Y' means this product is recyclable and 'N' means it is not.   Write an SQL query to find the ids of products that are both low fat and recyclable. Return the result table in  any order . The query result format is in the following example.   Example 1: Input: Products table: +-------------+----------+------------+ | product_id | low_fats | recyclable | +-------------+----------+------------+ | 0 | Y | N | | 1 ...