Rob Renzetti กำกับซีรีส์กี่เรื่อง?ไม่จำเป็นต้องใช้ตารางทั้งหมด
How many series were directed by Rob Renzetti?It is not neccessary to use all the tables.
 table_18734298_1:  (no_in_series [ VARCHAR ] directed_by [ VARCHAR) ]
SELECT COUNT(no_in_series) FROM table_18734298_1 WHERE directed_by = "Rob Renzetti"