Question

我想知道如何解决这个问题，我有这两个表：

TABLE FRIENDSHIP
Name | Friend
--------------
John | Mark
Peter | Paul
Simon | Mary

TABLE SCHOOL
Name | School
--------------
John | SchoolA
Mark | SchoolA
Peter | SchoolB
Paul | SchoolC
Simon | SchoolC
Mary | SchoolD

如何选择那些朋友但不参加同一所学校的人？我想选择计数为＆lt; 2的第一所学校，然后将这些人的名字与FRIENDSHIP表中的名字进行比较（比较两个名称和朋友的名字）。如何将其转换为查询？对不起是一个新手..

应该给我回复：

Name | Friend
---------------
Peter | Paul
Simon | Mary

感谢您的帮助

Answer 1

您可以尝试将SCHOOL表加入FRIENDSHIP两次，对于该对中的每个朋友一次。然后，您可以通过仅保留各自的学校不相同的朋友对来限制您的结果集。

SELECT f.Name, f.Friend
FROM FRIENDSHIP f INNER JOIN SCHOOL s1 ON f.Name = s1.Name
INNER JOIN SCHOOL s2 ON f.Friend = s2.Name
WHERE s1.School <> s2.School

以下是使用您的示例数据进行此查询的工作演示：

SQLFiddle

Answer 2

SELECT F.Name, F.Friend
FROM Friendship F
INNER JOIN School AS School1 ON F.Name = School1.Name
INNER JOIN School AS School2 ON F.Friend = School2.Name
WHERE School1.School <> School2.School

编辑：根据实际架构修改

SELECT C.Name, C.Colleague
FROM Collaboration C
INNER JOIN restaurant_founder AS rf1 ON C.Name = rf1.founder
INNER JOIN restaurant_founder AS rf2 ON C.Colleague = rf2.founder
WHERE rf1.restaurant <> rf2.restaurant

Answer 3

你可以这样做：

select * from friend f
where (select s2.school from school s2
       where f.name = s2.name) != (select s1.school from school s1
                                  where f.friend = s1.name)

这是Demo

Answer 4

您的示例中有两种类型的人。

我们将第一个称为Name，将第二个称为Friend。

Name和Friend都有School。

我们需要比较他们的School是不同的，所以我们需要首先获得他们的School。

让School加入Name

，让Friend.Name获得School.Name

SELECT f.Name, School, f.Friend 
FROM Friend AS f
INNER JOIN School AS s ON f.Name = s.Name

现在，让School加入Friend

，让Friend.Friend获得School.Name

SELECT Friend, School 
FROM Friend AS f
INNER JOIN School AS s ON f.Friend = s.Name

现在我们得到了SchoolOfName和SchoolOfFriend的结果，让Friend SchoolOfName和Friend SchoolOfFriend

此外，School的{{1}}不应等于SchoolOfName的{{1}}

School

计数后的SQL查询公共值

4 个答案: