A       B      C
1 client_id name  purchase_ids
2         1 jim
3         2 bob
4         3 bill


purchase_id purchase_client_id amount
          1                  1    100
          2                  1    500
          3                  2     50

=CONCATENATE(A1, "-", B1) # returns "foo-bar" if A1 has 'foo' and B1 has 'bar'