Customers_Who_Never_Order.sql

PROBLEM:

183. Customers Who Never Order

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  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+
Orders table:
+----+------------+
| id | customerId |
+----+------------+
| 1  | 3          |
| 2  | 1          |
+----+------------+
Output: 
+-----------+
| Customers |
+-----------+
| Henry     |
| Max       |
+-----------+





SOLUTION:

# Write your MySQL query statement below
#Here's my solution
#by Parul Sharma

#1.
select C.Name as Customers
from Customers C left join Orders O on C.ID = O.CustomerID
where if(O.ID,0,1)


#2.
SELECT name as Customers
from Customers
where id not in (
    select customerId
    from Orders
);


#3.
SELECT Name AS Customers
FROM CUSTOMERS
LEFT JOIN ORDERS
ON ORDERS.CustomerID = Customers.Id
WHERE Orders.CustomerID IS NULL