Sql 如何计算数据并列出数据

我对SQL非常陌生

例如，一个有2个As和3个Cs的学生将产生两个记录：sid，a，2；希德，C，3。如果学生没有任何成绩，我不想把他们列出来

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

我想要的示例：

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

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我想这应该对你有用

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;

如果它看起来令人困惑，请尝试单独运行内部查询以查看其功能：

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