Question

急，急，急 pl/sql ,oracle 根据查询结果统计数量

有一张表 student_mart,有一下字段信息 ，
project：科目，值为语文、数学、英语
mark：成绩，值为A、B、C、D
现在要求写一个效率不错的sql：统计这张表中语文成绩为D的条数，数学成绩为D的条数，英语成绩为D的条数。
提问没有提好，不好意思各位。
在加一个字段：calssno :班级。我想统计出下面的这个种结果。

Answer 1

select A.calssno, A.count_1, B.count_2, C.count_3
from
(select count(*) as count_1, calssno
from student_mart
where project = '语文'
and mark = 'D'
group by calssno) A,
(select count(*) as count_2, calssno
from student_mart
where project = '数学'
and mark = 'D'
group by calssno) B,
(select count(*) as count_3, calssno
from student_mart
where project = '英语'
and mark = 'D'
group by calssno) C
where A.calssno = B.calssno
and B.calssno = C.calssno

Answer 2

SELECT calssno, 语文成绩为A的条数=COUNT(CASE WHEN project='语文' AND mark='A' THEN 1 END),数学成绩为B的条数=COUNT(CASE WHEN project='数学' AND mark='B' THEN 1 END),
英语成绩为C的条数=COUNT(CASE WHEN project='英语' AND mark='C' THEN 1 END)
FROM student_mart

GROUP BY calssno

Answer 3

select count(*) from student_mart where mark='D' and project='语文'

union

select count(*) from student_mart where mark='D' and project='数学'
union

select count(*) from student_mart where mark='D' and project='英语'

Answer 4

select project,count(*) from student_mart t where t.mark='D' group by t.project