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