Question

我需要计算在2个mysql列中找到结果的次数。

实施例

|  Column A   |  Column B   |
|   white     |    black    |
|   black     |    green    |
|   orange    |    white    |
|   black     |    blue     |

我需要得到这个结果：

white -> 2 times
black -> 3 times
green -> 1 time
orange -> 1 time
blue -> 1 time

我为单列做了它，它起作用了：

SELECT 
    column_name
    , COUNT(column_name) as total 
FROM table_name 
WHERE (......) 
GROUP BY column_name 
HAVING column_name != '' 
ORDER BY total DESC

我无法理解它如何适用于2列

Answer 1

对于您的特定用途，我会做这样的事情：

SELECT col, COUNT(col) FROM
    (SELECT columnA as col FROM table
       UNION ALL SELECT columnB FROM table) as tmp_table
WHERE ... GROUP BY ... HAVING ... ORDER BY ...

Answer 2

尝试使用UNION ALL子句，在内部查询中选择所需的所有内容（意味着，在嵌套查询中保留WHERE子句）

SELECT
    column_nameA
    ,count(*) AS total
FROM(
    SELECT 
        column_nameA
    FROM table_name 
    WHERE (......) 

    UNION ALL 

    SELECT 
        column_nameb
    FROM table_name 
    WHERE (......) 
)a 
GROUP BY column_nameA
HAVING column_name != '' 
ORDER BY 1

将结果计入2个mysql列

2 个答案: