Question

我在MySQL中有一张包含学生成绩的表格。我想发出一个单个SQL查询，该查询将从所有列（例如

adNumber |Eng | Kis| Math| Phys| chem
1254     | A  | B  | B   | A   | D
2147     | B  | A  | A   | A   | C
3241     | D  | A  | C   | A   | E

我想得到类似以下的内容：

Eng| kIS| Math | Phys | chem
1  | 2  |  1   |   3  |  0

当我发出要从所有列中计数“ A”的语句时。我将不胜感激。

Answer 1

您可以在以下情况下使用一种情况：或if和一个选择

    select sum(case when Eng  = 'A' then 1 else 0 end) as Eng
        , sum(case when Kis  = 'A' then 1 else 0 end) as Kis
        , sum(case when Math  = 'A' then 1 else 0 end) as Math
        , sum(case when Phys  = 'A' then 1 else 0 end) as Phys
        , sum(case when Chem  = 'A' then 1 else 0 end) as Chem
    from Grades

Answer 2

您可以通过子查询来实现

select 
    (Select count(*) from Grades where Eng = 'A') as Eng,
    (Select count(*) from Grades where Kis = 'A') as Kis,
    (Select count(*) from Grades where Math = 'A') as Math,
    (Select count(*) from Grades where Phys = 'A') as Phys,
    (Select count(*) from Grades where Chem = 'A') as Chem

Answer 3

尝试此查询：

select sum(case when Eng = 'A' then 1 else 0 end) Eng,
       sum(case when Kis = 'A' then 1 else 0 end) Kis,
       sum(case when Math = 'A' then 1 else 0 end) Math,
       sum(case when Phys = 'A' then 1 else 0 end) Phys,
       sum(case when chem = 'A' then 1 else 0 end) chem
from Grades

MySQL在几列中计数值

3 个答案: