Distance from maximum value for each distance - sql

Question

I would like to calculate the distance to maximum value for each possible distance. As an example:
Row Distance Value
1 1 2 --> 1 (Distance from Row 1)
2 2 3 --> 2 (Distance from Row 2)
3 3 3 --> 2 (Distance from Row 2)
4 4 1 --> 2 (Distance from Row 2)
5 5 5 --> 5 (Distance from Row 5)
6 6 1 --> 5 (Distance from Row 5)
Explanation: Row 6 has value of 5 because the first occurrence of maximum value between rows 1 through 6 was at distance 5.
I have tried to use some windows functions but cannot figure out how to put it together.
Sample data:
--drop table tmp_maxval;
create table tmp_maxval (dst number, val number);
insert into tmp_maxval values(1, 3);
insert into tmp_maxval values(2, 2);
insert into tmp_maxval values(3, 1);
insert into tmp_maxval values(4, 2);
insert into tmp_maxval values(5, 4);
insert into tmp_maxval values(6, 2);
insert into tmp_maxval values(7, 2);
insert into tmp_maxval values(8, 5);
insert into tmp_maxval values(9, 5);
insert into tmp_maxval values(10,1);
commit;
Functions I think can be useful in solving this:
select t.*,
max(val) over(order by dst),
case when val >= max(val) over(order by dst) then 1 else 0 end ,
case when row_number() over(partition by val order by dst) = 1 then 1 else 0 end as first_occurence
from
ap_risk.tmp_maxval t

Answer 1

select dst, val,
max(case when flag is null then dst end) over (order by dst)
as first_occurrence
from (
select dst, val,
case when val <= max(val) over (order by dst
rows between unbounded preceding and 1 preceding)
then 1 end as flag
from tmp_maxval
)
order by dst
;
DST VAL FIRST_OCCURRENCE
---------- ---------- ----------------
1 3 1
2 2 1
3 1 1
4 2 1
5 4 5
6 2 5
7 2 5
8 5 8
9 5 8
10 1 8
Or, if you are on Oracle version 12.1 or higher, MATCH_RECOGNIZE can do quick work of this assignment:
select dst, val, first_occurrence
from tmp_maxval t
match_recognize(
order by dst
measures a.dst as first_occurrence
all rows per match
pattern (a x*)
define x as val <= a.val
)
order by dst
;

Answer 2

You can get the maximum value using a cumulative max:
select mv.*, max(mv.value) over (order by mv.distance) as max_value
from ap_risk.tmp_maxval mv;
I think this answers your question. If you want the distance itself:
select mv.*,
min(case when max_value = value then distance end) over (order by distance) as first_distance_at_max_value
from (select mv.*, max(mv.value) over (order by mv.distance) as max_value
from ap_risk.tmp_maxval mv
) mv;

Answer 3

You could use either max() or min() combined with case when:
select t.*,
min(case when val = mv then dst end) over (partition by mv order by dst) v1,
max(case when val = mv then dst end) over (partition by mv order by dst) v2
from (select t.*, max(val) over (order by dst) mv from tmp_maxval t) t
order by dst
Result:
DST VAL MV V1 V2
---------- ---------- ---------- ---------- ----------
1 3 3 1 1
2 2 3 1 1
3 1 3 1 1
4 2 3 1 1
5 4 4 5 5
6 2 4 5 5
7 2 4 5 5
8 5 5 8 8
9 5 5 8 9
10 1 5 8 9
Explained logic and words first occurence suggest that you need min(), but third row in your example suggest max() ;-) In data which you provided you can observe difference in rows 9-10. Choose what you want.