如何獲得學生證的學生那裏得到了A級，但不是C

Question

表 .......

student_id Grade 
1    A 
1    B 
1    D 
2    B 
2    C 
2    A 

所需的輸出 .............

student_id 
1 

我曾嘗試 ............

select student_id from student where grade='A' and not grade='c'; 

但我得到錯誤的輸出

Answer 1

按A的等級選擇，左加入等級student_id和等級C，並排除匹配項。

select distinct 
a.student_id 
from grades as a 
    left join grades as c 
    on c.student_id = a.student_id 
    and c.Grade = 'C' 
where a.Grade = 'A' 
and c.student_id is null -- exclude students with C's 

這是demo。

Answer 2

一個簡單的方法是聚集和一個having子句：

select student_id 
from student 
group by student_id 
having sum(case when grade = 'A' then 1 else 0 end) > 0 and 
     sum(case when grade = 'C' then 1 else 0 end) = 0;