key1   key2  key 3
v1     d1    t1
v2     d2    t1
v3     d1    t4
v1     d3    t8
v1     d2    t4

key1 v1 3
key1 v2 1
key1 v3 1
key2 d1 2

(select 'key1' AS column_origin, key1, count(key1) from TestTable group by key1)
union all
(select 'key2', key2, count(key2) from TestTable group by key2)
union all
(select 'key3', key3, count(key3) from TestTable group by key3);