我如何计算数据并列出数据

Question

我对SQL非常陌生

例如，一个具有2 As和3 C的学生将产生两条记录：sid，A，2； sid，C，3。如果学生没有任何成绩，我不想列出他们

select sid, count(grade) from enrollments
group by sid

我想要的例子：

sid          grade
123          A,2; C,3
456          A,3; B,1

Answer 1

我认为这应该对您有用。

select sid, 
    listagg(gradecount, '; ') within group (order by gradecount) as grade
from (
    select sid, grade || ',' || count(1) as gradecount
    from enrollments
    where grade is not null
    group by sid, grade
    ) studentgradecount
group by sid;

如果看起来令人困惑，请尝试单独运行内部查询以查看其作用：

select sid, grade || ',' || count(1) as gradecount
from enrollments
where grade is not null
group by sid, grade