JOIN查询以从另一个表中检索多个列引用到单个列

Question

下面是我的数据库图表，其中包含三个表及其关系 - PersonalInfo，Subjects，Students

目前，Students表的值低于此值。

我正在尝试查询要显示的数据如下。

我尝试了什么

SELECT FullName, SubjectName AS 'Subject1', SubjectName AS 'Subject2',
SubjectName AS 'Subject3', SubjectName AS 'Subject4',SubjectName AS 'Subject5' 
FROM Subjects JOIN Students ON Students.Subject1 =Subjects.Id 
JOIN PersonalInfo ON PersonalInfo.Id=Students.StudId

获取低于输出的错误。它只显示第一个主题的名称。

任何人都可以以正确的方式指导我。

Answer 1

您必须加入每个主题的多个时间。 “Sudent”和“PersonalInfo”表格ID和外键存在混淆。所以请根据设计加入。下面的查询将根据您的需要为您提供所有主题名称。请将查询视为逻辑。我可能会在此处输入语法错误

Select SUB1.SubejctName as Subject1,SUB2.SubejctName as Subject2,SUB3.SubejctName as Subject3,SUB4.SubejctName as Subject4,SUB5.SubejctName as Subject5, from Students S 
    inner join Subjects SUB1 on SUB1.id=S.Subject1
    inner join Subjects SUB2 on SUB2.id=S.Subject2
    inner join Subjects SUB3 on SUB3.Id=S.Subject3
    inner join Subjects SUB4 on SUB4.id=S.Subject4
    inner join Subjects SUB5 on SUB5.Id=S.Subject5

Todo - 加入PersonalInfo表以显示学生姓名。

Answer 2

工作查询

SELECT FullName, 
sb.SubjectName AS 'Subject1', 
sb2.SubjectName AS 'Subject2',
sb3.SubjectName AS 'Subject3', 
sb4.SubjectName AS 'Subject4',
sb5.SubjectName AS 'Subject5' 
FROM Students s 
JOIN PersonalInfo ON PersonalInfo.Id=s.StudId
JOIN Subjects sb ON s.Subject1 =sb.Id 
JOIN Subjects sb2 ON s.Subject2 =sb2.Id 
JOIN Subjects sb3 ON s.Subject3 =sb3.Id 
JOIN Subjects sb4 ON s.Subject4 =sb4.Id
JOIN Subjects sb5 ON s.Subject5 =sb5.Id

<强>结果

https://www.w3schools.com/css/css_table.asp