mysql - 为什么 sum() 函数在这种情况下没有给出确切的值?
问题描述
select s_id, s_f_name, s_l_name, s_roll_no, s_class,
SUM(mid_1_english + mid_2_english)/2 as mid_english,
SUM(mid_1_mathematics + mid_2_mathematics)/2 as mid_mathematics,
semester_final_english,
semester_final_mathematics,
SUM((mid_1_english + mid_2_english)/2 + semester_final_english) as total_english,
SUM((mid_1_mathematics + mid_2_mathematics)/2 + semester_final_mathematics) as total_mathematics,
SUM((mid_1_mathematics + mid_2_mathematics)/2 + (mid_1_english + mid_2_english)/2 + semester_final_mathematics + semester_final_mathematics) as total
from elaborate_term_result_sheet
group by s_f_name, s_l_name
order by s_roll_no;
运行创建的此查询后,它确实显示了输出,但值有点波动
mid_1_english + mid_2_english = mid_english
mid_1_mathematics + mid_2_mathematics = mid_mathematics
mid_english + term_final_english = total_english
mid_mathematics + term_final_mathematics = total_mathematics
总计 = total_english + total_mathematics
解决方案
select s_id, s_f_name, s_l_name, s_roll_no, s_class,
SUM(mid_1_english + mid_2_english)/2 as mid_english,
SUM(mid_1_mathematics + mid_2_mathematics)/2 as mid_mathematics,
semester_final_english,
semester_final_mathematics,
SUM((mid_1_english + mid_2_english)/2 + semester_final_english) as total_english,
SUM((mid_1_mathematics + mid_2_mathematics)/2 + semester_final_mathematics) as total_mathematics,
SUM((mid_1_english + mid_2_english)/2 + semester_final_english + (mid_1_mathematics + mid_2_mathematics)/2 + semester_final_mathematics) as total from result_sheet_1 group by s_f_name, s_l_name order by s_roll_no;
提供正确输出的唯一更改是
SUM((mid_1_english + mid_2_english)/2 + semester_final_english + (mid_1_mathematics + mid_2_mathematics)/2 + semester_final_mathematics) as total
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