SubQuery hatasini nasil cozerim?

Merhaba.Query:

Select product as name, (Select WEIGHT from order_log where weight_const is null)as metbex from order_log;

Error: ORA-01427: single-row subquery returns more than one row. SubQuery birden cox netice qaytariyor ondan kaynaklaniyor.Amma nasil bunu hall ederim?