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 use a union query

SELECT x.f1,Count(x.f1) FROM
(SELECT p1 As F1 FROM table
 UNION ALL
 SELECT p2 As F1 FROM table
 UNION ALL
 SELECT p3 As F1 FROM table) x
GROUP BY x.f1