Question

以下是我的表：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，指向学校所属的学校主键。与指向其所属Kid主键的Class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id和姓名记录。它还包括他们的学校名称和姓名。

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

您只需使用JOIN即可。做类似的事情：

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

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 3

如果所有的孩子实体最终都会映射到学校，那么您正在寻找的是内部联接。可能需要不同的JOIN，否则可以是LEFT或RIGHT join。

SELECT kids.id，kids.name，schools.id，schools.name FROM kids INNER JOIN classes ON kids.class_id = classes.id INNER JOIN SCHOOL on schools.id = classes.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

跨多个表的SQL select语句

4 个答案: