Aggregation by positive/negative values v.2 - sql

Question

I've posted several topics and every query had some problems :( Changed table and examples for better understanding
I have a table called PROD_COST with 5 fields
(ID,Duration,Cost,COST_NEXT,COST_CHANGE).
I need extra field called "groups" for aggregation.
Duration = number of days the price is valid (1 day=1row).
Cost = product price in this day.
-Cost_next = lead(cost,1,0).
Cost_change = Cost_next - Cost.
example:
+----+---------+------+-------------+-------+
|ID |Duration | Cost | Cost_change | Groups|
+----+---------+------+-------------+-------+
| 1 | 1 | 10 | -1,5 | 1 |
| 2 | 1 | 8,5 | 3,7 | 2 |
| 3 | 1 | 12.2 | 0 | 2 |
| 4 | 1 | 12.2 | -2,2 | 3 |
| 5 | 1 | 10 | 0 | 3 |
| 6 | 1 | 10 | 3.2 | 4 |
| 7 | 1 | 13.2 | -2,7 | 5 |
| 8 | 1 | 10.5 | -1,5 | 5 |
| 9 | 1 | 9 | 0 | 5 |
| 10 | 1 | 9 | 0 | 5 |
| 11 | 1 | 9 | -1 | 5 |
| 12 | 1 | 8 | 1.5 | 6 |
+----+---------+------+-------------+-------+
Now i need to group("Groups" field) by Cost_change. It can be positive,negative or 0 values.
Some kind guy advised me this query:
select id, COST_CHANGE, sum(GRP) over (order by id asc) +1
from
(
select *, case when sign(COST_CHANGE) != sign(isnull(lag(COST_CHANGE)
over (order by id asc),COST_CHANGE)) and Cost_change!=0 then 1 else 0 end as GRP
from PROD_COST
) X
But there is a problem: If there are 0 values between two positive or negative values than it groups it separately, for example:
+-------------+--------+
| Cost_change | Groups |
+-------------+--------+
| 9.262 | 5777 |
| -9.262 | 5778 |
| 9.262 | 5779 |
| 0.000 | 5779 |
| 9.608 | 5780 |
| -11.231 | 5781 |
| 10.000 | 5782 |
+-------------+--------+
I need to have:
+-------------+--------+
| Cost_change | Groups |
+-------------+--------+
| 9.262 | 5777 |
| -9.262 | 5778 |
| 9.262 | 5779 |
| 0.000 | 5779 |
| 9.608 | 5779 | -- Here
| -11.231 | 5780 |
| 10.000 | 5781 |
+-------------+--------+
In other words, if there's 0 values between two positive ot two negative values than they should be in one group, because Sequence: MINUS-0-0-MINUS - no rotation. But if i had MINUS-0-0-PLUS, than GROUPS should be 1-1-1-2, because positive valus is rotating with negative value.
Thank you for attention!
I'm Using Sql Server 2012

Answer 1

I think the best approach is to remove the zeros, do the calculation, and then re-insert them. So:
with pcg as (
select pc.*, min(id) over (partition by grp) as grpid
from (select pc.*,
(row_number() over (order by id) -
row_number() over (partition by sign(cost_change)
order by id
) as grp
from prod_cost pc
where cost_change <> 0
) pc
)
select pc.*, max(groups) over (order by id)
from prod_cost pc left join
(select pcg.*, dense_rank() over (order by grpid) as groups
from pcg
) pc
on pc.id = pcg.id;
The CTE assigns a group identifier based on the lowest id in the group, where the groups are bounded by actual sign changes. The subquery turns this into a number. The outer query then accumulates the maximum value, to give a value to the 0 records.