SQL last status change date - sql

Question

I am trying to get the dates of last status changes. Below is an example data table.
In brief I want to query the minimum DATE value of the latest STATUS (ordered by CHANGE_NO) for each PRODUCT_ID. Mentioned values are the ones filled with yellow.
So far, I could get only the latest dates for each product.
SELECT
*
FROM
(
SELECT
PRODUCT_ID, CHANGE_NO, STATUS, DATE
,MAX(CHANGE_NO) OVER(PARTITION BY PRODUCT_ID) MAX_CHANGE_NO
FROM TABLE
ORDER BY PRODUCT_ID, CHANGE_NO
)
WHERE MAX_CHANGE_NO = CHANGE_NO
Please kindly share the link if there is already a question/answer for a similar case; I've searched but couldn't find any.
Note: I am using Oracle SQL.
Thanks in advance.

Answer 1

Here's one way to do this with analytic functions (avoiding joins).
with
test_data ( product_id, change_no, status, dt ) as (
select 1, 1, 'A', date '2016-10-10' from dual union all
select 1, 2, 'B', date '2016-10-11' from dual union all
select 1, 3, 'C', date '2016-10-12' from dual union all
select 1, 4, 'D', date '2016-10-13' from dual union all
select 2, 1, 'Y', date '2016-02-02' from dual union all
select 2, 2, 'X', date '2016-02-03' from dual union all
select 2, 3, 'X', date '2016-02-04' from dual union all
select 3, 1, 'H', date '2016-06-20' from dual union all
select 3, 2, 'G', date '2016-06-21' from dual union all
select 3, 3, 'T', date '2016-06-22' from dual union all
select 3, 4, 'K', date '2016-06-23' from dual union all
select 3, 5, 'K', date '2016-06-24' from dual union all
select 3, 6, 'K', date '2016-06-25' from dual
)
-- End of test data (not part of the solution). SQL query begins below this line.
select product_id,
max(status) keep (dense_rank last order by change_no) as status,
max(dt) as dt
from (
select product_id, change_no, status, dt,
case when lead(status) over (partition by product_id
order by change_no desc)
= status then 0 else 1 end as flag
from test_data
)
where flag = 1
group by product_id
order by product_id -- if needed
;
Output
PRODUCT_ID STATUS DT
---------- ------ ----------
1 D 13/10/2016
2 X 03/02/2016
3 K 23/06/2016

Answer 2

SELECT * FROM (
SELECT PRODUCT_ID, CHANGE_NO, STATUS,DATE, MIN(DATE) OVER(PARTITION BY PRODUCT_ID,STATUS) as MIN_DATE_OF_LATEST_STATUS
FROM (SELECT PRODUCT_ID, CHANGE_NO, STATUS, DATE
,FIRST_VALUE(STATUS) OVER(PARTITION BY PRODUCT_ID ORDER BY CHANGE_NO DESC) LATEST_STATUS
FROM TABLE
) T
WHERE STATUS = LATEST_STATUS
) T
WHERE DATE = MIN_DATE_OF_LATEST_STATUS
Use the FIRST_VALUE window function to get the latest status for each product_id
Get the MIN date for those status rows
Finally get those rows where min_date = date
If change_no isn't needed in the final result, the query can be simplified to
SELECT PRODUCT_ID, STATUS, MIN(DATE) as MIN_DATE_OF_LATEST_STATUS
FROM (SELECT PRODUCT_ID, CHANGE_NO, STATUS, DATE
,FIRST_VALUE(STATUS) OVER(PARTITION BY PRODUCT_ID ORDER BY CHANGE_NO DESC) LATEST_STATUS
FROM TABLE
) T
WHERE STATUS = LATEST_STATUS
GROUP BY PRODUCT_ID, STATUS