In this Leetcode Customers Who Never Order problem solution Suppose that a website contains two tables, the Customers table, and the Orders table. Write a SQL query to find all customers who never order anything.

Leetcode Customers Who Never Order problem solution


Problem solution in Oracle.

select Name as "Customers"
from Customers Left Join Orders 
ON Customers.Id = Orders.CustomerId
where Orders.CustomerId is null;



Problem solution in Mysql.

SELECT A.Name As Customers
FROM Customers A
WHERE NOT EXISTS
(SELECT B.CustomerId FROM Orders B WHERE B.CustomerId = A.Id)


Problem solution in TSQL.

SELECT A.Name AS Customers
FROM Customers AS A 
LEFT JOIN Orders AS B 
ON A.Id = B.CustomerID
WHERE B.CustomerID IS NULL