Question

这是我的选择陈述：

SELECT lastName + ',' + firstName as Name,  
       classNumber
FROM STUDENT 
RIGHT JOIN ENROLL ON Enroll.stuid = Student.stuid

和输出：

name           classnumber
--------------------------
Smith,Tom      ART103A  
Smith,Tom      HST205A  
Chin,Ann       ART103A  
Chin,Ann       CSC201A  
Chin,Ann       MTH103A  
McCarthy,Owen  ART103A   
McCarthy,Owen  MTH103C  
Rivera,Jane    CSC201A  
Rivera,Jane    MTH101B

我希望这样每个名字只出现在第一列一次。任何帮助或想法都非常感激。

Answer 1

由于行彼此独立，因此没有行可以知道它是否是第一行。

你可以做的是GROUP BY Name并将所有classNumbers放在一个像这样的列表中：

SELECT lastName + ',' + firstName AS Name,
       GROUP_CONCAT(classNumber SEPARATOR '\n') AS classNumbers
FROM student
RIGHT JOIN Enroll ON (Student.stuid = Enroll.stuid)
GROUP BY Name

Answer 2

如果只出现一个班级。

SELECT lastName + ',' + firstName as Name, classNumber
FROM STUDENT 
RIGHT JOIN 
(select Student.stuid as stuid, min(classNumber) as ClassNumber 
 from ENROLL Enroll inner Join Student
 ON (Student.stuid = Enroll.stuid) group by Student.stuid) AS NewEnrol 
 ON NewEnroll.stuid = Student.stuid

或者

SELECT lastName + ',' + firstName as Name,Min(classNumber)
FROM STUDENT 
RIGHT JOIN ENROLL ON Enroll.stuid = Student.stuid
Group By lastname+','+firstname

在SQL中格式化输出，以便列b的多个值与列a的一个值相关联

2 个答案: