Question

我想编写一个SQL查询，列出所有班级中有三（3）名以上学生的教师（在本例中为Mrs. Smith）。我最初认为HAVING子句是实现此目的的正确方法，但我没有按预期提出Mrs. Smith。

Teacher         Student
-------------------------
Mrs. Smith      Danny
Mrs. Smith      Emily
Mrs. Smith      Todd
Mrs. Smith      Paul
Mr. French      Sam
Mr. French      Carol
Mr. French      Patty

SELECT DISTINCT Teacher
FROM Students 
HAVING (COUNT(Teacher) > 3)
GROUP BY Teacher, Student

Answer 1

使用HAVING是正确的，你只需要正确使用它

SELECT Teacher
FROM Students 
GROUP BY Teacher
HAVING COUNT(Student) > 3

基本上，您将教师记录分组在一起，同时计算每位教师拥有的学生的数量。并按此计算过滤。

Answer 2

是的，HAVING是正确的。尝试：

SELECT Teacher
FROM Students 
GROUP BY Teacher
HAVING (COUNT(1) > 3)

Answer 3

我认为你只需要在最后放置HAVING条款：

SELECT DISTINCT Teacher
FROM Students 
GROUP BY Teacher, Student
HAVING COUNT(Teacher) > 3;

Answer 4

所有教师具有 超过三名学生

所以：

select teacher, count(student) --All Teachers
FROM Students 
GROUP BY Teacher
HAVING COUNT(student) > 3  --Having more than three students

Answer 5

由教师将其更改为仅分组，并在分组后添加

SELECT Teacher
FROM Students    
GROUP BY Teacher
HAVING (COUNT(Teacher) > 3)

使用带有COUNT的HAVING来限制结果

5 个答案: