Question

以上是我要解决的问题。首先，我想尝试在SQL中使用EXCEPT子句，并获取Orders表中不存在的所有值。我正在尝试的是：（暂时忽略列名和内容，我只想测试EXCEPT逻辑）

SELECT Id, Name FROM Customers
EXCEPT
SELECT O.CustomerId as Id, C.Name AS Name FROM Customers C , Orders O
WHERE C.Id = O.CustomerId

但是，我在LeetCode上收到此错误，我不确定：

Line 3: SyntaxError: near 'SELECT O.CustomerID as Id, C.Name AS Name FROM Customers C , Orders O WHERE C.Id'

我要从编写的查询中获得的预期输出是：

Id    Name
2     Henry
4     Max

编辑：这是LeetCode的问题，在查看使用的版本后，我发现它是mysql-server 5.7.21

Answer 1

如果您坚持使用EXCEPT，请设置为EXCEPT ALL：

SELECT Id FROM Customers
EXCEPT ALL
SELECT CustomerID FROM Orders;

但是我宁愿使用LEFT JOIN / .. IS NULL：

SELECT C.*
FROM   Customers C
LEFT   JOIN Orders O ON O.CustomerId = C.Id
WHERE  O.CustomerId IS NULL;

请参阅：

Select rows which are not present in other table

Answer 2

我看到您的dbms是mysql。 Mysql不支持EXCEPT

另一种尝试使用NOT IN的方法比EXCEPT容易

模式（MySQL v5.7）

CREATE TABLE  Customers(
   id int,
   Name varchar(50)
);

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

CREATE TABLE  Orders(
   id int,
   CustomerId int
);

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

查询＃1

SELECT Id, Name 
FROM Customers
WHERE Id NOT IN (
   SELECT O.CustomerID
   FROM Orders O 
);

| Id  | Name  |
| --- | ----- |
| 2   | Henry |
| 4   | Max   |

View on DB Fiddle

如果您的dbms支持EXCEPT，则我将使用JOIN而不是,连接两个表，因为JOIN 连接两个表的语义更清晰。

SELECT Id, Name 
FROM Customers
EXCEPT
SELECT O.CustomerID as Id, C.Name AS Name
FROM Customers C JOIN Orders O ON C.Id = O.CustomerID

使用EXCEPT子句时出现错误

2 个答案: