183. 从不订购的客户—not in()、左连接
题目：题目描述链接
解题：
解法一：not in()
SELECT Name AS 'Customers'
FROM Customers
WHERE Id not in (
SELECT CustomerId FROM Orders
)
解法二：左连接
SELECT a.Name AS 'Customers'
FROM Customers a
LEFT JOIN Orders b
On a.Id = b.CustomerId
WHERE b.CustomerId is NULL
注意：
WHERE b.CustomerId is NULL
容易写错
WHERE b.CustomerId = NULL