LeetCode--183.从不订购的客户

建表

Create table If Not Exists Customers (Idint, Name varchar(255));
Create table If Not Exists Orders (Id int,CustomerId int);
Truncate table Customers;
insert into Customers (Id, Name) values('1', 'Joe');
insert into Customers (Id, Name) values('2', 'Henry');
insert into Customers (Id, Name) values('3', 'Sam');
insert into Customers (Id, Name) values('4', 'Max');
Truncate table Orders;
insert into Orders (Id, CustomerId) values('1', '3');
insert into Orders (Id, CustomerId) values('2', '1');

两表联查，根据Customers进行左连接查询，找CustomerId为空的

select c.*
 from customers c left join orders o
 on c.Id = o.CustomerId where CustomerId is null