显示学生总数[关闭]

Question

显示所有科目和帮助材料的学生总数

student (rollNumber, Sfname, Slname, email,phone)
Subjects(Subid, subTitle, credit_hrs)
std_sub(rollNUmber (fk from student), subid(fk frim subjects), session, sectionID)

我写了查询

select subTitle,Subid,rollNumber,rollNUmber 
from student s 
join std_sub st on s.rollNumber=st.rollNUmber 
join subjects sub on sub.subid=st.subid 

但还是需要修改

Answer 1

如果我的理解正确，那么您想找出每个主题的 total_students。

Count() 将显示每个学科的学生人数，如果任何学科没有学生，那么它将显示 0 作为学生数

select 
    subTitle,
    Subid,
    coalesce(count(st.rollNumber), 0) as total_students

from subjects sub 

left join std_sub st 
on sub.subid = st.subid 

left join student s
on st.rollNumber = s.rollNUmber

group by 
    subTitle,
    Subid

没有入学的学生

select
    rollNumber,
    Sfname,
    Slname
from student
where rollNumber not in (
    select
        distinct rollNumber
    from std_sub
)