Moving sum with dates for teradata - teradata

Question

I have a situation where I have to create a moving sum for the past 6 months. My data looks like
A B 20-Jan-18 20
A B 20-Mar-18 45
A B 10-Apr-18 15
A B 21-May-18 30
A B 30-Jul-18 10
A B 15-Aug-18 25
And the expected result is
A B 20-Jan-18 20 20 Sum of row1
A B 20-Mar-18 45 65 Sum of row1+2
A B 10-Apr-18 15 80 Sum of row1+2+3
A B 21-May-18 30 110 Sum of row1+2+3+4
A B 30-Jul-18 10 100 Sum of row2+3+4+5 (as row1 is > 6 months in the past)
A B 15-Aug-18 25 125 Sum of row2+3+4+5+6
I tried to use the solution proposed in an earlier thread by inserting dummy records for dates where there is no record and then using ROWS BETWEEN 181 PRECEDING AND CURRENT ROW
But there may be situations where there are multiple records on the same day which means that choosing the last 181 rows will lead to the earliest record getting dropped.
I have checked a lot of cases on this forum and others but can't find a solution for this moving average where the window size is not constant. Please help.

Answer 1

Teradata doesn't implement RANGE in Windowed Aggregates, but you can use old-style SQL to get the same result. If the number of rows per group is not too high it's very efficient, but needs an intermediate table (unless the GROUP BY columns are the PI of the souce table). The self-join on the PI columns results in an AMP-local direct join plus aggregated locally, without matching PIs it will be a less efficient join plus aggregated globally
create volatile table vt as
( select a,b,datecol,sumcol
from mytable
) with data
primary index(a,b);
select t1.a, t1.b, t1.datecol
,sum(t2.sumcol)
from vt as t1
join vt as t2
on t1.a=t2.a
and t1.b=t2.b
and t2.datecol between t1.datecol -181 and t1.datecol
group by 1,2,3
Of course this will not work as expected if there are multiple rows per day (this will increase the number of rows for the sum due to the n*m join). You need some unique column combination, this defect_id might be useful.
Otherwise you need to switch to a Scalar Subquery which takes care about non-uniqueness, but is usually less efficient:
create volatile table vt as
( select a,b,defect_id,datecol,sumcol
from mytable
) with data
primary index(a,b);
select t1.*
,(select sum(t2.sumcol)
from vt as t2
where t1.a=t2.a
and t1.b=t2.b
and t2.datecol between t1.datecol -181 and t1.datecol
)
from vt as t1
To use your existing approach you must aggregate those multiple rows per day first