Question 8: MySQL ---------- Duplicate Emails, email

Question 8: MySQL ---------- Duplicate Emails, email

Suppose that a website contains two tables,CustomersTable andOrdersTable. Write a SQL query to find all customers who never order anything.

Table:Customers.

+----+-------+| Id | Name  |+----+-------+| 1  | Joe   || 2  | Henry || 3  | Sam   || 4  | Max   |+----+-------+

Table:Orders.

+----+------------+| Id | CustomerId |+----+------------+| 1  | 3          || 2  | 1          |+----+------------+

Using the above tables as example, return the following:

+-----------+| Customers |+-----------+| Henry     || Max       |+-----------+

Answer:

SELECT A.Name from Customers AWHERE A.Id NOT IN (SELECT B.CustomerId from Orders B)

You can also write the following two methods:

SELECT A.Name from Customers AWHERE NOT EXISTS (SELECT 1 FROM Orders B WHERE A.Id = B.CustomerId)SELECT A.Name from Customers ALEFT JOIN Orders B on  a.Id = B.CustomerIdWHERE b.CustomerId is NULL