Question

无法提出正确的查询来计算学生总人数

我有三张桌子：

学生 - 包含男性或女性的学生档案

2.student_attendance - 包含学生是否在场的出勤细节＆＃34; 0＆＃34;或＆＃34; 1＆＃34;

出勤 - 包含所有会议详情，其中一个学生可以参加一个课程。

我需要计算一个会议现在或缺席的男孩/女孩的数量。

我的主要问题是将这些逻辑解释为sql

if(in_attendace =1) then 
    sum the number of boys as boys_present
    sum the number of girls as girls_present
else
    sum the number of boys as boys_absent
    sum the number of girls as girls_absent

select 
case when a.in_attendance = 1 then
SUM(CASE b.gender when 1 then 1 else 0 end ) as male_present,
SUM(CASE b.gender when 2 then 1 else 0 end ) as female_present,
ELSE
SUM(CASE b.gender when 1 then 1 else 0 end ) as male_absent,
SUM(CASE b.gender when 2 then 1 else 0 end ) as female_absent
END
from attendance_student  as a inner join student as b on a.student_id = b.id where a.session_details_id = 38

Answer 1

嗯，你离解决方案不是很远，你只需要将它们分成不同的列（我认为这就是你想要的）：

select COUNT(CASE WHEN a.in_attendance = 1 and b.gender = 1 then 1 END) as male_present,
       COUNT(CASE WHEN a.in_attendance = 1 and b.gender = 2 then 1 END) as female_present,
       COUNT(CASE WHEN a.in_attendance = 0 and b.gender = 1 then 1 END) as male_absent,
       COUNT(CASE WHEN a.in_attendance = 0 and b.gender = 2 then 1 END) as female_absent
FROM attendance_student a
INNER JOIN student b
 ON a.student_id = b.id 
WHERE a.session_details_id = 38

sql计算出现和缺席的男孩和女孩

1 个答案: