Count results in 2 mysql column

Question

I need to count how many times a result is found in 2 mysql column.

Ex.

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

I need to get this result:

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

I did it for single column and it works:

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

I can't understand how it can works with 2 columns

Answer 1

For your particular use, I would do something like this:

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

Try it with a UNION ALL clause, selecting all which you need in the inner query (meaning, keep the WHERE clause in the nested query)

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