SQL select with case when and join table

I have 2 table in sql (postgresql)

tbl1 :

dates	roomid	stok
2021-03-15	A01	3
2021-03-16	A01	3
2021-03-17	A01	3

tbl2 :

bookingcode	startdate	enddate	roomid
B001	2021-03-15	2021-03-17	A01

My syntax like this

select dates, tbl1.roomid,
case
    when dates between startdate and enddate - integer '1' then stok -1
else stok
end stok
from tbl1
join tbl2
on tbl1.roomid = tbl2.roomid  order by dates asc

When the number of booking is one (tbl2), it matches results like this . The results are correct

dates	roomid	stok
2021-03-15	A01	2
2021-03-16	A01	2
2021-03-17	A01	3

But when the booking is 2, it’s like this (tbl2)

bookingcode	startdate	enddate	roomid
B001	2021-03-15	2021-03-17	A01
B002	2021-03-15	2021-03-17	A01

The result is like this, the results are not suitable

dates	roomid	stok
2021-03-15	A01	2
2021-03-15	A01	2
2021-03-16	A01	2
2021-03-16	A01	2
2021-03-17	A01	3
2021-03-17	A01	3

The results I want when booking 2 are like this

dates	roomid	stok
2021-03-15	A01	1
2021-03-16	A01	1
2021-03-17	A01	3

Can anyone come up with a solution?

Answer

If you need to update the database just do

UPDATE tbl1 SET stok = stok - (SELECT COUNT(*) FROM tbl2 WHERE tbl1.roomid = tbl2.roomid AND tbl1.dates >= tbl2.startdate AND tbl1.dates < tbl2.enddate);

otherwise do

SELECT dates, roomid, stok - (SELECT COUNT(*) FROM tbl2 WHERE tbl1.roomid = tbl2.roomid AND tbl1.dates >= tbl2.startdate AND tbl1.dates < tbl2.enddate) FROM tbl1;