Group price with start and end date - sql

Question

I have a table
Recordid Price Start date end date
-----------------------------------------
1 20 2017-10-01 2017-10-02
2 20 2017-10-03 2017-10-04
3 30 2017-10-05 2017-10-05
4 20 2017-10-06 2017-10-07
I want to get every price when it started and when it ended so my result set would be
20. 2017-10-01. 2017-10-04
30. 2017-10-05. 2017-10-05
20. 2017-10-06. 2017-10-07
I'm having problems to figure it out
It's an Oracle database

Answer 1

i figured it out with the code below
SELECT distinct price
, case when start_dt is null then lag(start_dt) over (order by start_date)
else start_dt end realstart
, case when end_dt is null then lead(end_dt) over (order by end_date)
else end_dt end realend
FROM (SELECT case when nvl(lag(price) over (order by start_date),-1) <> price then start_date end start_dt
, case when nvl(lead(price) over (order by end_date),-1) <>price then end_date end end_dt
, price
, start_date
, end_date
FROM t) main
WHERE start_dt is not null
or end_dt is not null

Answer 2

From your sample data I think you want to have start date and end date whenever the price has been changed in order of the record id.
The following query may contain more sub queries than neccessary, because readability. The very inner select determines when the price has been changed here called group changes. The Next level froms the group by a rolling sum. This is possible, because the only the group change contains values > 0. The rest is obvious.
SELECT GRP,
PRICE,
MIN("Start date") AS "Start date",
MAX("end date") AS "end date"
FROM ( SELECT sub.*,
SUM(GROUP_CHANGE) OVER (ORDER BY RECORDID) AS GRP
FROM ( SELECT t.*,
CASE
WHEN RECORDID = LAG(t.RECORDID) OVER (ORDER BY t.PRICE, t.RECORDID) + 1
THEN 0
ELSE RECORDID
END AS GROUP_CHANGE
FROM t ) sub ) fin
GROUP BY GRP, PRICE
ORDER BY GRP
GRP PRICE Start date end date
---------- ---------- ---------- --------
1 20 01.10.17 04.10.17
4 30 05.10.17 05.10.17
8 20 06.10.17 11.10.17
Tested with following data (Note that I have add some record to your deliverd sample data as I wanted to have a group with three records)
CREATE TABLE t (
Recordid INT,
Price INT,
"Start date" DATE,
"end date" DATE
);
INSERT INTO t VALUES (1, 20, TO_DATE('2017-10-01', 'YYYY-MM-DD'), TO_DATE('2017-10-02', 'YYYY-MM-DD'));
INSERT INTO t VALUES (2, 20, TO_DATE('2017-10-03', 'YYYY-MM-DD'), TO_DATE('2017-10-04', 'YYYY-MM-DD'));
INSERT INTO t VALUES (3, 30, TO_DATE('2017-10-05', 'YYYY-MM-DD'), TO_DATE('2017-10-05', 'YYYY-MM-DD'));
INSERT INTO t VALUES (4, 20, TO_DATE('2017-10-06', 'YYYY-MM-DD'), TO_DATE('2017-10-07', 'YYYY-MM-DD'));
INSERT INTO t VALUES (5, 20, TO_DATE('2017-10-08', 'YYYY-MM-DD'), TO_DATE('2017-10-09', 'YYYY-MM-DD'));
INSERT INTO t VALUES (6, 20, TO_DATE('2017-10-10', 'YYYY-MM-DD'), TO_DATE('2017-10-11', 'YYYY-MM-DD'));

Answer 3

Here is one method that might work in your case:
select price, min(start_date), max(end_date)
from (select t.*,
sum(case when prev_price = price and prev_end_date = start_date - 1
then 0 else 1
end) over (order by t.start_date) as grp
from (select t.*,
lag(t.end_date) over (order by t.start_date) as prev_end_date,
lag(t.price) over (order by t.start_date) as prev_price
from t
) t
) t
group by price, grp