SQL减去2个子查询 - 编程之家

如何解决SQL减去2个子查询

对 sql 相当陌生，我想看看我是否可以获得减法方面的帮助。我想减去 studenttaken - studentnotreviewed，然后将别名总数分配给操作。我在想一些事情

select ((select count(*) from students where exams.id=students.exam_id) - (select count(*) from students where exams.id=students.exam_id and (students.review_flag='' or students.review_flag is null)) ) as 'Total'

但是我不太确定会遇到一些语法问题。

select x.* from
(

select schools.name as School,exams.name as name,exams.exam_start as examstart,exams.exam_end as examend,(select count(*) from students where exams.id=students.exam_id) as studentstaken,(select count(*) from students where exams.id=students.exam_id and (students.review_flag='' or students.review_flag is null)) as studentsnotreviewed,#select () as 'Total'
case when exam_end< (Now() - interval 2 day) then 'Yes' else 'No' end as 'Overdue',exam_end + Interval 2 day as 'DueDate',(select value from exam_options where exams.id=exam_options.exam_id and option_id=5) as IDtoggle,(select value from exam_options where exams.id=exam_options.exam_id and option_id=6) as Roomscantoggle
from exams
left join taggables on exams.school_id=taggable_id
left join schools on exams.school_id=schools.id
where tag_id=12 and exam_start < Now() and exam_start>'2021-01-01' and practice=0) as x
where studentsnotreviewed>0 and (studentsnotreviewed>15 or examend < Now())  and (IDtoggle=1 or Roomscantoggle=1)
order by duedate asc,studentsnotreviewed desc

[样本数据]

学校	姓名	考试开始	考试	学生参与	studentsnotreviewed	IDtoggle	Roomscannetoggel
德克萨斯大学休斯顿健康科学学院	考试一	2021 年 2 月 3 日上午 10:55	2021 年 2 月 3 日下午 1:30	26	2	1	1
德克萨斯大学休斯顿健康科学学院	考试一	2021 年 2 月 4 日上午 10:45	2021 年 2 月 4 日下午 12:59，上午 12:59	31	1	1	1

[想要的结果]

学校	姓名	考试开始	考试	学生参与	studentsnotreviewed	总计	IDtoggle	Roomscannetoggel
德克萨斯大学休斯顿健康科学学院	考试一	2021 年 2 月 3 日上午 10:55	2021 年 2 月 3 日下午 1:30	26	2	24	1	1
德克萨斯大学休斯顿健康科学学院	考试一	2021 年 2 月 4 日上午 10:45	2021 年 2 月 4 日下午 12:59，上午 12:59	31	1	30	1	1

解决方法

应该没问题。

select x.* 
from
(
    select schools.name as School,exams.name as name,exams.exam_start as examstart,exams.exam_end as examend,(select count(*) from students where exams.id=students.exam_id) as studentstaken,(select count(*) from students where exams.id=students.exam_id and (students.review_flag='' or students.review_flag is null)) as studentsnotreviewed,(select count(*) from students where exams.id=students.exam_id) 
        - (select count(*) from students where exams.id=students.exam_id and (students.review_flag='' or students.review_flag is null)) as 'Total',... rest of the query