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