对两列进行查询，就好像它们是一列

问题描述

| 有2列包含相同类型的数据：

col_a  col_b ...
Bob    Tim   ..
John   Frank .
Bob    John
John   Tim
Bob    Bob
Frank  John

现在我要执行的查询是这样的（计数出现次数：（Bob，3），（John，2），..）：

SELECT col_a,count(*) AS total FROM table1 GROUP BY col_a

但是，我不想在col_a上同时运行它，而是想同时在col_a和col_b上运行它（（Bob，4），（John，4），..） 任何帮助表示赞赏 编辑：     谢谢大家。 再次感谢     

解决方法

Select Z.name,Count(*) As Total
From    (
        Select col_a As name
        From total
        Union All
        Select col_b
        From total
        ) As Z
Group By Z.name

    ,

select Name,count(*) as Total
from (
    select col_a as Name from MyTable
    union all
    select col_b from MyTable
) a
group by Name

    ,根据您的“ 4”列，我认为您需要对子查询进行分组：

select idx,sum(count)
from (
    select col_a as idx,count(*) as count
    from table
    union all
    select col_b as idx,count(*) as count
    where col_a <> col_b -- avoid dups
    ) as counts
group by idx

要么：

select idx,count(*)
from (
    select col_a as idx
    from table
    union all
    select col_b as idx
    where col_a <> col_b -- avoid dups
    ) as counts
group by idx