join(q,r,s,p)

q(A int, D char(15))
1, 'e'
1, 'g'
2, 'f'
3, 'e'

r(A int, B char(10))
1, 'a'
2, 'a'
2, 'c'
3, 'b'

s(B char(10), C int)
'a', 2
'a', 4
'b', 5
'd', 3

p(C int, D char(15))
2, 'e'
2, 'f'
5, 'g'

result(A int, D char(15), B char(10), C int)
1, 'e', 'a', 2
2, 'f', 'a', 2