Question

假设我有三张桌子

Student     Student_Interest     Interest
=======     ================     ========
Id          Student_Id           Id
Name        Interest_Id          Name

Student_Interest.Student_Id指的是Student.Id 和Student_Interest.Interest_Id指的是Interest.Id

假设我们有三种兴趣即。 “Java”，“C”，“C ++”和“C＃”，学生表中有一些条目以及Student_Interest表中各自的兴趣映射条目。（典型的多对多关系）

我们如何才能获得同时兼顾“Java”和“C”的学生名单？

Answer 1

只需从student_interest获取Java和C记录，按学生分组，看看您是否获得了学生的完整兴趣数量。通过这些学生发现，您可以显示学生表中的数据。

select *
from student
where id in
(
  select student_id
  from student_interest
  where interest_id in (select id from interest where name in ('Java', 'C'))
  group by student_id
  having count(distinct interest_id) = 2
);

编辑：您已经让我用EXISTS显示查询。直截了当的方式是：

select *
from student
where exists
(
  select * 
  from student_interest
  where student_id = student.id
  and interest_id = (select id from interest where name = 'Java')
)
and exists
(
  select * 
  from student_interest
  where student_id = student.id
  and interest_id = (select id from interest where name = 'C')
);

对于每个兴趣，还有一个额外的EXISTS条款。但是，如果要将上面的IN查询转换为EXISTS查询，那么只有一个EXISTS子句，则得到：

select *
from student
where exists
(
  select student_id
  from student_interest
  where student_id = student.id
  and interest_id in (select id from interest where name in ('Java', 'C'))
  group by student_id
  having count(distinct interest_id) = 2
);

我发现IN子句更具可读性，但我认为这是一种品味问题。

Answer 2

我已经看到了几个正确答案，但无论如何，这是我的答案：

select s.* from student s   
join (
    select si.student_id from student_interest si join interest i on i.id = si.interest_id
    where i.name in ('Java','C') group by si.student_id having count(*) = 2   
) iv on iv.student_id = s.id

Answer 3

您需要加入所有三个表格以获取如下信息：

SELECT s.*
FROM Student s, Student_Interest si, Interest i, Interest sin
WHERE s.Id = si.Student_Id
AND   i.Id = si.Interest_Id
AND   sin.Id = si.Interest_Id
AND   i.Name = 'Java'
AND   sin.Name =  'C'

Answer 4

对所有表格执行JOIN。您需要GROUP BY列Name才能获得如下所示的兴趣。查看演示小提琴http://sqlfiddle.com/#!2/e80391/13

select s.Name
from student s
join Student_Interest si on s.id = si.Student_Id
join Interest i on si.Interest_Id = i.id
join Interest ii on si.Interest_Id = ii.id
group by s.Name
having count(*) > 1

Answer 5

我们如何获得同时具有“Java”和“C”的学生列表他们的兴趣？

我们可以写t（t.c，...）来表示行（t.c，...）在表t中。让别人学生为s，学生_Interest为sij和sic以及对ij和ic的兴趣。我们想要行（s.Id，s.Name）其中

    s(s.Id,s.Name)
AND sij(sij.Student_Id,sij.Interest_Id) AND s.Id = sij.Student_Id
AND sic(sic.Student_Id,sic.Interest_Id) AND s.Id = sic.Student_Id
AND ij(ij.Id,ij.Name) AND ij.Id=sij.Interest_Id AND ij.Name = 'Java'
AND ic(ic.Id,ic.Name) AND ic.Id=sic.Interest_Id AND ic.Name = 'C'

所以：

select s.Id,s.Name
from Student s
join Student_Interest sij on s.Id = sij.Student_Id
join Student_Interest sic on s.Id = sic.Student_Id
join Interest ij on ij.Id=sij.Interest_Id AND ij.Name = 'Java'
join Interest ic on ic.Id=sic.Interest_Id AND ic.Name = 'C'

将一列中的一个值与SQL中其他列中的多个值匹配

5 个答案: