order
id    model   amount  preprint  void
1     20      20      0         0
2     21      30      0         0

model
no    partno
20    testmodel20
21    testmodel21

serials
sn        order   user
test1     1       1
test2     1       1
test3     1       1
test4     2       1
test5     2       0



alles
id    partno        count   amount  preprint  void
1     testmodel20   3       20      0         0
2     testmodel21   1       30      0         0

count: serials.order = order.id AND serials.user <> 0