How to calculate average when you use "rel_date_diff"

Content

How to calculate average working hours between two dates

Example: I´v this report: 

assign_acct_ID	ref_no	DATE1	DATE2	rel_date_diff(DATE2,DATE1,1)
Jhon Lara	151223-000026	xxxxx	xxxx	30:00:00
Jhon Lara	151115-000125	xxxx	xxxx	20:00:00

And, I need any like this:

assign_acct_ID	AVG(rel_date_diff(DATE2,DATE1,1))
Jhon Lara	25:00:00

are there other way to do this whithout the function AVG()?? becouse, the "rel_date_dif" can not is into the other function.

 

Regards

Version

Oracle service cloud August 2015 SP2 (Build 141)