Average time to resolve report - all techs

Hello - searching the forums here I'm just not quite finding the exact query I'm looking for. We recently migrated to ServiceDesk Plus from our old on prem spiceworks.

Needing help creating a simple Average time to resolve query, this is what I used to run in Spiceworks that used SQLite:

SELECT DATE(Created_at, 'Start of month') as 'Start of month',

ROUND(avg(julianday(ifnull(closed_at,'now'))-julianday(created_at)),2)

AS "Time to Resolve" FROM tickets where priority = '2'

GROUP BY DATE(tickets.created_at, 'Start of month')

Perhaps someone could assist converting this to work in SDP? We are running the PGSQL database option.

I am basically just looking to run a query each month to track and report on our "average time to close" for medium priority service requests. Need the average time to be expressed in days. Typically I have to run this for 12 months at a time and do a look back as when tickets were closed that spanned multiple months that would impact the report calculations.

Thanks much for any feedback