SQL, count in multiple columns then group by

Question

I am trying to count in multiple columns then group by for a total sum where the same data appears in any column

Source data table:

P1  P2  P3
-----------
a         


        

Answer 1

You can union all the records in a subquery and on the outer query, count each value.

SELECT b.a, COUNT(b.a)
FROM
    (
        SELECT P1 a
        FROM tableName
        UNION ALL
        SELECT P2 a
        FROM tableName
        UNION ALL
        SELECT P3 a
        FROM tableName
    ) b
GROUP BY b.a