mysqli每次工作仅在其他条件下，但在没有条件的情况下不工作 [英] mysqli every time work only else condition but not if condition

问题描述

这是我的查询

CREATE VIEW marksheet as
SELECT name as name, student_id as student_id, 
roll as roll, class as class,exam_year as exam_year, 
subject_name as subject, exam_type as exam_type,
sum(full_mark) as full_mark, sum(getmark) as getmark,
department as department,
IF(SUM(IF(gpa='f' OR gpa='F',-9999,gpa))>=0, 
CAST(IF(subject_type=1,SUM(gpa)-2/count(subject_name),SUM(gpa)/count(subject_name)) 
AS CHAR), 'F') as total_gpa
FROM mark
GROUP by roll, class, exam_type

不起作用

IF(subject_type=1,SUM(gpa)-2/count(subject_name),SUM(gpa)/count(subject_name))

每次只能工作else条件SUM(gpa)/count(subject_name

不起作用subject_type=1,SUM(gpa)-2/count(subject_name)

我的桌子

结果:gpa = 5 + 8 + 4 + 6

Result : gpa = 5+8+4+6

         = 23

但是subject_type = 1 so ,minus -2(无效)

But subject_type = 1 so ,minus -2 (not work)

         = 21 (Not work)

最终Gpa = 21/count(subject_name)

Final Gpa = 21/count(subject_name)

推荐答案

如果只有一个额外的主题(即具有subject_type=1的主题)而所有其他主题都具有subject_type=0，则可以使用MAX(subject_type)确定如果学生选修了额外的科目.该查询应该执行您想要的操作(请注意，您还需要在SUM(gpa)-2周围加上()):

If there can be only one extra subject (i.e. subject with subject_type=1) and all other subjects have subject_type=0, you can use MAX(subject_type) to determine if a student took an extra subject. This query should do what you want (note that you also need () around SUM(gpa)-2):

CREATE VIEW marksheet as
SELECT name as name, student_id as student_id, 
roll as roll, class as class,exam_year as exam_year, 
subject_name as subject, exam_type as exam_type,
sum(full_mark) as full_mark, sum(getmark) as getmark,
department as department,
IF(SUM(IF(gpa='f' OR gpa='F',-9999,gpa))>=0, 
CAST(IF(MAX(subject_type)=1,(SUM(gpa)-2)/count(subject_name),SUM(gpa)/count(subject_name)) 
AS CHAR), 'F') as total_gpa
FROM mark
GROUP by roll, class, exam_type

我已经在 SQLFiddle 中创建了一个简化的演示.

I've created a simplified demo at SQLFiddle.

这篇关于mysqli每次工作仅在其他条件下，但在没有条件的情况下不工作的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！