View difference between Paste ID: K2WDtbDx and Q5nrEx9A

--- https://pgexercises.com/questions/date/daysinmonth.html
+-- https://pgexercises.com/questions/date/utilisationpermonth.html
--- date_part does not work for the second column of the second clause, but date_trunc does
+-- longer than the recommended solution, but more transparent IMO
 
-with gs as (select generate_series(
+-- count available slots per month
-	  '2012-01-01'::timestamp,
+with t1 as (
-	  '2012-12-31'::timestamp,
+	select
-	  '1 month'::interval) as month)
+		date_trunc('month',starttime) as month,
 		25*LEFT(((DATE_TRUNC('month', starttime)+'1 month'::INTERVAL)-DATE_TRUNC('month', starttime))::TEXT,2)::INTEGER AS len_int
-select date_part('month', month) as m,
+		from cd.bookings
-		(date_trunc('month', month)+'1 month'::INTERVAL)-date_trunc('month', month) as len
+		group by 1, 2),
-from gs
+
 -- count used slots per month per facility
 t2 as(
 	select f.name,
 		date_trunc('month',starttime) as month,
 		sum(slots) as used_slots
 		from cd.bookings b
 		join cd.facilities f
 		on f.facid = b.facid
 		group by 1, 2
 		order by 1 asc, 2 asc
 ),
 
 -- line up facility, month, available slots, used slots
 t3 as (
 	select 	name,
 			t.month,
 			len_int,
 			sum(used_slots) as usedslots
 	from t1 t
 	join t2 d
 	on t.month = d.month
 	group by 1, 2, 3
 	order by name asc
 )
 -- finally divide one by the other
 select name, month, ROUND(100*(usedslots/len_int),1) as uti
 from t3