Average sum with start end end date - sql

Question

I'm working with SQL Teradata and I have a table as such:
cust_id start_dt end_dt amount is_current_y_n
12345 1/8/2018 7/8/2018 7044 N
12345 7/9/2018 7/10/2018 8142 N
12345 7/11/2018 7/13/2018 7643 N
12345 7/14/2018 7/14/2018 8630 N
12345 7/14/2018 7/19/2018 5597 N
12345 7/20/2018 12/31/9999 5680 Y
Another case that I've seen:
cust_id start_dt end_dt amount is_current_y_n
54321 1/1/2015 12/31/9999 8650 Y
I need to calculate with SQL the average amount for the past:
7 days
30 days
90 days
180 days
"Average", meaning that if during the past 7 days the amount changed from 1000 to 2000 in the 3rd day, the average should be:
(1000x3 + 2000x4)/7
I tried to join the table with a date table but it's not very efficient.
Is there any efficient way to achieve that?

Answer 1

It can probably be done via Recursive Common Table Expression Query.
To unfold those date ranges.
With the amounts for each date, the CTE can be joined back to the table to get those averages.
I couldn't test the SQL on a TeraData (don't have it).
But it should almost work on that RDBMS (probably)
WITH RECURSIVE CTE (cust_id, dt, amount, start_dt, end_dt) AS
(
SELECT cust_id, start_dt as dt, amount, start_dt,
case when end_dt - start_dt > 4200 then start_dt else end_dt end
FROM table_as_such
UNION ALL
SELECT cust_id, dt+1, amount, start_dt, end_dt
FROM CTE
WHERE dt < end_dt
)
SELECT t.cust_id, t.start_dt
, ROUND(AVG(case when CTE.dt between t.start_dt - 7 and t.start_dt then CTE.amount end),2) as avg7
, ROUND(AVG(case when CTE.dt between t.start_dt - 30 and t.start_dt then CTE.amount end),2) as avg30
, ROUND(AVG(case when CTE.dt between t.start_dt - 90 and t.start_dt then CTE.amount end),2) as avg90
, ROUND(AVG(case when CTE.dt between t.start_dt - 180 and t.start_dt then CTE.amount end),2) as avg180
FROM table_as_such t
JOIN CTE ON (CTE.cust_id = t.cust_id AND CTE.dt between t.start_dt - 180 and t.start_dt)
GROUP BY t.cust_id, t.start_dt
ORDER BY t.cust_id, t.start_dt;
Sample Data Used:
create table table_as_such (id int not null primary key, cust_id int, start_dt date, end_dt date, amount int, is_current_y_n char(1));
insert into table_as_such values (1,12345,'2018-01-08','2018-07-08',7044,'N');
insert into table_as_such values (2,12345,'2018-07-09','2018-07-10',8142,'N');
insert into table_as_such values (3,12345,'2018-07-11','2018-07-13',7643,'N');
insert into table_as_such values (4,12345,'2018-07-14','2018-07-14',8630,'N');
insert into table_as_such values (5,12345,'2018-07-14','2018-07-19',5597,'N');
insert into table_as_such values (6,12345,'2018-07-20','9999-12-31',5680,'Y');

Answer 2

maybe the temporal feature of Teradata can help you in this case. This is due to the PERIOD datatyp and the function to expand.
check this example for this feature and your intention:
database demo;
create table demoDateExpand (
myID integer
,myUser VARCHAR(100)
,myAmount DECIMAL(10,2)
,startDT DATE
,endDT DATE
) no primary index;
insert into demoDateExpand values (1, 'User01', 2.5, '2018-01-01', '2018-01-05');
insert into demoDateExpand values (2, 'User01', 3.0, '2018-01-08', '2018-01-15');
insert into demoDateExpand values (3, 'User01', 1.5, '2018-01-11', '2018-01-25');
insert into demoDateExpand values (4, 'User02', 2.0, '2018-01-01', '2018-01-15');
insert into demoDateExpand values (5, 'User02', 2.5, '2018-01-05', '2018-01-25');
insert into demoDateExpand values (6, 'User02', 4.5, '2018-01-26', '2018-01-27');
insert into demoDateExpand values (7, 'User03', 1.0, '2018-01-10', '2018-01-15');
insert into demoDateExpand values (8, 'User03', 3.5, '2018-01-16', '2018-01-25');
select myID
,myUser
,myAmount
,startDT
,endDT
,period(startDT, endDT)
from demoDateExpand
;
select myID
,myUser
,myAmount
,BEGIN(myDate)
from demoDateExpand
expand on period(startDT, endDT) AS myDate BY ANCHOR DAY
order by myID, myDate
;

Answer 3

I managed to create my own query with the help of a table with dates:
2017-07-11
2017-07-12
...
My query is:
sel
c.cust_id
,avg(case when c.cal_dt between '2017-07-01' and '2018-01-01' then c.amount end) as avg_180
,avg(case when c.cal_dt between '2017-10-01' and '2018-01-01' then c.amount end) as avg_90
,avg(case when c.cal_dt between '2017-12-01' and '2018-01-01' then c.amount end) as avg_30
,avg(case when c.cal_dt between '2017-12-24' and '2018-01-01' then c.amount end) as avg_7
from
(
sel b.cust_id
,a.cal_dt
,b.amount
from
(
sel *
from CALENDAR_DAILY_TABLE
where cal_dt between '2017-07-01' and '2018-01-01'
) as a
join
(
sel *
from MY_TABLE
where (start_dt > '2017-07-01' or end_dt='9999-12-31')
) as b
on b.start_dt<=a.cal_dt and a.cal_dt<=b.end_dt
) as c
where c.cust_id ='12345'
group by c.cust_id
The result is:
cust_id avg_180 avg_90 avg_30 avg_7
12345 1.34 1.34 1.34 1.34
Thanks!