Retrieving Detailed Calculation in a group by query

Question

I am writing a query that has a calculation based on an ID column or every detailed record in the table, but the output/report needs to be grouped by another column. The calculation is days_open/count(*). The days_open column is a field in the table.
The output should be
Case Type Avg_days_open
A 20
B 31
C 34
D 55
The days open column in the table is structured like this:
ID Days_Open
1 34
2 10
3 23
My query below is retrieving dupes per case type.
select a. case_type_cd,
days_between_sum/count(*) avg_days_pending
from tab a,(select distinct case_type_cd, Days_Between days_between_sum from tab ) d
WHERE FILED_DT between to_date(:BEGIN_Dt,'mm/dd/yyyy') and to_date(:END_Dt,'mm/dd/yyyy')
and reporting_nr like :RID and federal_state = :FEDERAL_STATE
and description is null
and d.case_type_cd(+) = a.case_type_cd
GROUP BY a.case_type_cd, days_between_sum

Answer 1

Case Type case_nbr determination_dt Filed_dt
A 123 10/02/2005 09/09/2005
B 222 09/01/2004 07/01/2004
C 094 01/01/2006 11/23/2005