编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE Customers (
	id int,
	name varchar(255)
);
CREATE TABLE Orders (
	id int,
	customerId int
    );

INSERT INTO Customers VALUES (1, 'Joe');
INSERT INTO Customers VALUES (2, 'Henry');
INSERT INTO Customers VALUES (3, 'Sam');
INSERT INTO Customers VALUES (4, 'Max');

INSERT INTO Orders VALUES(1,3);
INSERT INTO Orders VALUES(2,1);


explain select C.name as Customers from Customers as C where not exists(select 1 from Orders as 
O where C.id=O.customerId);