mysql - 跨多个表的 SQL 选择语句

Question

这是我的表：School Class Kid。

每个班级属于一所学校。

每个孩子属于一个班级。

所有表都有一个自动递增的主键。

Class有一个外键指向它所属的学校的主键。与Kid指向Class它们所属的主键相同。

如果我想select kid.id, kid.name, school.id, school.name如何在一个查询中执行此操作？

此结果将返回每个孩子的记录及其 id 和 name。它还将包括他们的学校 ID 和姓名。

SCHOOL
------     
id-primary     
eyname

CLASS
-----
id-primary key         
school_id-foreign key to school name

KID
---
id-primary key           
class_id-foreign key to class name

Answer 1

你只需要使用JOIN. 执行以下操作：

SELECT kid.id, kid.name, school.id, school.keyname
FROM kid
JOIN class on class.id = kid.class_id
JOIN school on school.id = class.school_id

你也可以这样做：

SELECT kid.id, kid.name, school.id, school.name
FROM kid, class, school
WHERE class.id = kid.class_id and school.id = class.school_id

Answer 2

如果所有孩子实体最终都将映射到学校，那么您正在寻找的是 INNER JOIN。可能需要不同的 JOIN，否则它是 LEFT 或 RIGHT 连接。

SELECT kids.id、kids.name、schools.id、schools.name FROM kids INNER JOIN classes ON kids.class_id = classes.id INNER JOIN school ONschools.id = classes.school_id;

Answer 3

Select kid.id,kid.Name,school.Id,school.keyname
From kid
Inner join Class On k.Class_id = Class.Id
Inner join School On Class.school_id = school.id

Answer 4

select s.*, c.*, k.* 
from school s 
left join class c on c.school_id=s.id
left join kid k on k.class_id=c.id