Compare one value with other values within a group SQL Server - sql

Question

I have below table where column names are Item, Point and IsCorrect.
Item | Point | IsCorrect | Not actual column, just logic
-----+-------+-----------+--------------------
1 | 5 | 0 | 5 >= 6
1 | 8 | 0 | 8 >= 6
1 | 9 | 0 | 9 >= 6
1 | 6 | 1 | 6 >= 6
2 | 8 | 0 | 8 >= 7
2 | 7 | 1 | 7 >= 7
2 | 8 | 0 | 8 >= 7
2 | 9 | 0 | 9 >= 7
3 | 2 | 0 | 2 >= 9
3 | 5 | 0 | 5 >= 9
3 | 8 | 0 | 8 >= 9
3 | 9 | 1 | 9 >= 9
I want to first group by Item, get a Point value where IsCorrect = 1, compare it with other point values (as shown in 4th column). If all condition matched within a group, then select that item. I am expecting following result.
Item | Point | IsCorrect
-----+-------+----------
2 | 8 | 0
2 | 7 | 1
2 | 8 | 0
2 | 9 | 0
I want to use partition, not group by. Thank you so much for your help.

Answer 1

Window functions come to mind:
select t.*
from (select t.*,
max(case when iscorrect = 1 then point end) over (partition by item) as point_correct,
min(point) over (partition by item) as min_point
from t
) t
where min_point >= point_correct;
You could also do this with a subquery. Something like this:
select t.*
from t
where t.item in (select t2.item
from t t2
group by t2.item
having min(t2.point) >= min(case when t2.iscorrect then point end)
);
That is, for each item, compare the minimum point value to the "correct" point value.