Select Last Record Based on few criteria - sql

Question

Before
+--------+--------+---------+-------+------+
| RowNum | Status | Remarks | SetNo | |
+--------+--------+---------+-------+------+
| 1 | Q | | Set 1 | Want |
| 2 | Q | | Set 1 | Want |
| 3 | Q | | Set 1 | Want |
| 4 | Q | | Set 1 | Want |
| 5 | W | | Set 1 | Want |
| 1 | W | abc | Set 2 | |
| 2 | W | abc | Set 2 | |
| 3 | W | abc | Set 2 | |
| 4 | W | abc | Set 2 | Want |
| 1 | Q | | Set 3 | Want |
| 2 | w | abc | Set 3 | |
| 3 | w | abc | Set 3 | Want |
+--------+--------+---------+-------+------+
How to select Status=Q and Status=W based on Rownum=lastnumber and setno? Expectation result is the row with "want" is what i need. Those empty, will be remove
Tried:
select *
from mytable
where (RowNum != (select max(RowNum) from mytable) and status = 'W')

Answer 1

I understand that for each setno, you want all "Q"s and the latest "W". If so, you can use window functions like that:
select *
from (
select t.*,
row_number() over(partition by setno, status order by rownum desc) rn
from mytable t
) t
where rn = 1 or status = 'Q'

Answer 2

You might want to look into Window Functions. I don't fully understand what you need to do but I would suggest something like:
with rowNumberedData as
(
SELECT *,
ROW_NUMBER() OVER (PARTITION BY SetNo ORDER BY RowNum DESC) as RowOrder
FROM mytable
)
SELECT *
FROM rowNumberedData
WHERE (Status = 'Q' OR Status = 'W') AND RowOrder = 1
What this will do is add RowOrder column to your data and its value will be 1, for the max RowNum in every set. You can read more here and here to check what the with syntax is if you are unfamiliar.

Answer 3

This query should return the correct rows
with t_cte as (
select t.*,
row_number() over(partition by setno order by rownum desc) rn
from testTable t)
select *
from t_cte
where [status] = 'Q'
or ([status] = 'W'
and rn = 1);

Answer 4

I understand the question and wanting the last row for each set and then all rows with q. One method uses row_number():
select t.*
from (select t.*,
row_number() over (partition by setno order by rownum desc) as seqnum
from mytable t
) t
where seqnum = 1 or status = 'Q';
There are other ways to express this:
select t.*
from mytable t
where t.status = 'Q' or
t.rownum = (select max(t2.rownum)
from mytable t2
where t2.setno = t.setno
);
This is similar to the approach you are trying.