Count item across multiple columns in same table

Question

I have a table that looks like below

TableA

------------------------------------
id| ColumnA   | ColumnB   | ColumnC   
------------------------------------
1 | A        | B         | B      
2 | B        | D         | D
3 | C        | E         | A
------------------------------------

How to count the each of occurrence of each item in each column?

The result that I want is like below:

--------------------
Result    | Counter
--------------------
A         | 2
B         | 3
C         | 1
D         | 2
E         | 1

For single column I can use this SQL:

SELECT ColumnA, COUNT(*)
FROM TableA
GROUP BY ColumnA
HAVING COUNT(*) > 0

What about multiple column? Any help would be great!

Answer 1

Try this;)

select c as Result, count(1) as Counter from (
    select ColumnA c from TableA
    union all
    select ColumnB c from TableA
    union all
    select ColumnC c from TableA ) t
group by c

Answer 2

can can do it like this:

SELECT ColumnA as Result, sum(1) as Counter FROM (
  SELECT ColumnA FROM youTable
  UNION ALL
  SELECT ColumnB FROM youTable
  UNION ALL
  SELECT ColumnC FROM youTable
) AS res
GROUP BY ColumnA;