SQL Count In Range - sql

Question

How could I count data in range which could be configured
Something like this,
CAR_AVBL
+--------+-----------+
| CAR_ID | DATE_AVBL |
+--------------------|
| JJ01 | 1 |
| JJ02 | 1 |
| JJ03 | 3 |
| JJ04 | 10 |
| JJ05 | 13 |
| JJ06 | 4 |
| JJ07 | 10 |
| JJ08 | 1 |
| JJ09 | 23 |
| JJ10 | 11 |
| JJ11 | 20 |
| JJ12 | 3 |
| JJ13 | 19 |
| JJ14 | 22 |
| JJ15 | 7 |
+--------------------+
ZONE_CFG
+--------+------------+
| DATE | ZONE_DESCR |
+--------+------------+
| 15 | GREEN_ZONE |
| 25 | YELLOW_ZONE|
| 30 | RED_ZONE |
+--------+------------+
Table ZONE_CFG is configurable, so I could not use static value for this
The DATE column mean maximum date for each ZONE
And the result what I expected :
+------------+----------+
| ZONE_DESCR | AVBL_CAR |
+------------+----------+
| GREEN_ZONE | 11 |
| YELLOW_ZONE| 4 |
| RED_ZONE | 0 |
+------------+----------+
Please could someone help me with this

Answer 1

You can use LAG and group by as following:
SELECT
ZC.ZONE_DESCR,
COUNT(1) AS AVBL_CAR
FROM
CAR_AVBL CA
JOIN ( SELECT
ZONE_DECR,
COALESCE(LAG(DATE) OVER(ORDER BY DATE) + 1, 0) AS START_DATE,
DATE AS END_DATE
FROM ZONE_CFG ) ZC
ON ( CA.DATE_AVBL BETWEEN ZC.START_DATE AND ZC.END_DATE )
GROUP BY
ZC.ZONE_DESCR;
Note: Don't use oracle preserved keywords (DATE, in your case) as the name of the columns. Try to change it to something like DATE_ or DATE_START or etc..
Cheers!!

Answer 2

If you want the zero 0, I might suggest a correlated subquery instead:
select z.*,
(select count(*)
from car_avbl c
where c.date_avbl >= start_date and
c.date_avbl <= date
) as avbl_car
from (select z.*,
lag(date, 1, 0) as start_date
from zone_cfg z
) z;
In Oracle 12C, can phrase this using a lateral join:
select z.*,
(c.cnt - lag(c.cnt, 1, 0) over (order by z.date)) as cnt
from zone_cfg z left join lateral
(select count(*) as cnt
from avbl_car c
where c.date_avbl <= z.date
) c
on 1=1