reader: 57 bills still in the shop
one Select per bill:   owed Rp 1.529.000, 2954 questions, 56 ms
GetChildRows per bill: owed Rp 1.529.000, 1 load, 10 ms
Compute:               charged Rp 144.213.000 - received Rp 142.684.000 = Rp 1.529.000
