Question

SQL从多个表中选择并在其中一个表中应用不同的标准

第一张表：

 Student Name | Student ID
 --------------------------
   John Smith | 1
Marry Johnson | 2

第二张表：

Student ID | Year | Enrollment date
-----------------------------------
         1 | 2013 | 2013-10-01
         1 | 2014 | 2014-02-01
         2 | 2013 | 2013-10-01
         2 | 2014 | 2014-02-01

第三张表：

Student ID | Year | Class
---------------------------
         1 | 2013 | Math
         1 | 2013 | Spanish
         1 | 2013 | Art
         1 | 2014 | French
         2 | 2014 | Math
         2 | 2013 | Spanish
         2 | 2014 | Literature
         2 | 2014 | French
         2 | 2014 | Art

如何从[{1}}获取Name来自Table 1 + Year＆amp; Enrollment date Table 2的学生列表Math同年Art个课程？

 Student Name | Year | Enrollment date
 -------------------------------------
   John Smith | 2013 | 2013-10-01
Marry Johnson | 2014 | 2014-02-01

Answer 1

Select s.studentName, d.EnrollmentDate 
From firstTable s
   join thirdTable m 
       on m.StudentId = s.studentId
           and m.class = 'Math'
   join thirdTable 
       on a.StudentId = s.studentId
          and a.year = m.year              -- ensure that art is in same year as math
          and a.class = 'Art'
   join secondTable d
       on d.studentId = s.studentId
          and d.Year = m.year

或者，如果这是最近发布的SQL Server （支持基于values子句的动态结果集） - 这也解决了添加任意数量的附加类的问题

Select s.studentName, d.EnrollmentDate 
From firstTable s
   join secondTable d
       on d.studentId = s.studentId
          and d.Year = m.year 
Where Not exists 
    (Select * From (values ('Math'), ('Art')) c(class)
     where Not exists
         (Select * from thirdTable
          Where studentId = s.studentId
              and year = d.Year
              and class = c.class))

语法上，thios读作：

向我展示那些不一个班级（在提供的班级列表中）的学生，他们在同一年不注册

Answer 2

试试这个：

SELECT ft.student_name, st.Year, st.Enrollment_date from first_table ft
inner join second_table st on(ft.student_id = st.student_id) 
inner join third_table tt 
on(ft.student_id = tt.student_id and tt.class = 'Art')
inner join third_table tt1 
on(ft.student_id = tt1.student_id and tt1.class = 'Math'
 and tt.year = tt1.year) where tt.year = st.year

小提琴：http://sqlfiddle.com/#!2/c9e5e/1/0

Answer 3

如果我的评论是正确的，你想要的是让学生一起上课，那么这将有助于你获得一份清单。但是，我仍然不确定您如何链接到注册日期表。

select t1a.[student name] as Student1, t1b.[student name] as Student2 from
thirdtable t3a 
inner join thirdtable t3b on t3a.[Student ID]<t3b.[Student ID]
inner join firsttable t1a on t3a.[Student ID] = t1a.[Student ID]
inner join firsttable t1b on t1b.[Student ID] = t3b.[Student ID]
where t3a.class = t3b.class and t3a.year = t3b.year and t3a.class  in ('Art','Math')
group by t1a.[student name], t1b.[student name]
having count(*) > 1

Answer 4

决定是否使用WHERE子句或JOIN有时会很棘手。如果您使用的是允许使用INTERSECT的SQL版本，那么您还有更多选择。我会尝试：

 select t1.name, t2.year, t2.enrollment_date
 from table_1 t1 join table_2 t2 on t1.student_id = t2.student_id and t1.year = t2.year
 join (
      select student_id, year from t3 where class = 'Math'
      intersect
      select student_id, year from t3 where class = 'Art'
      ) fred on t1.student_id = fred.student_id and t1.year=fred.year

内部选择在这里非常通用;如果你愿意，你可以添加很多其他课程。如果INTERSECT不适合您的风格，那么其他推荐的加入将起作用。不过，我建议单独使用t3表作为子选择，然后将结果连接到表1和表2，因为它可以节省一些混乱：

 select t1.name, t2.year, t2.enrollment_date
 from table_1 t1 join table_2 t2 on t1.student_id = t2.student_id and t1.year = t2.year
 join (
      select t3_math.student_id, t3_math.year from table_3 t3_math
           join table_3 t3_art on t3_math.id = t3_art.id and t3_math.year = t3_art.year
           where t3_art.class = 'Art' and t3_math.class = 'Math'
      ) fred on t1.student_id = fred.student_id and t1.year=fred.year

SQL从多个表中进行选择，并在其中一个表中应用不同的条件

4 个答案: