Teradata - Split date range into month columns with day count - sql

Question

I need to split different date ranges over a quarter period into month columns with only the days actually used in that month. Each record (range) would be different.
Example:
Table
Record_ID Start_Date End_Date
1 10/27 11/30
2 11/30 12/14
3 12/14 12/31
Range 1 = 10/5 to 12/14
Range 2 = 11/20 to 12/31
Range 3 = 10/28 to 12/2
Output:
Range 1
Oct Nov Dec
27 30 14

Answer 1

Similar to #ULick's answer using sys_calendar.calendar, but a little more succinct:
CREATE VOLATILE MULTISET TABLE datetest (record_id int, start_date date, end_date date) ON COMMIT PRESERVE ROWS;
INSERT INTO datetest VALUES (1, '2017-10-05', '2017-12-14');
INSERT INTO datetest VALUES (2, '2017-11-20','2017-12-31');
SELECT record_id,
SUM(CASE WHEN month_of_year = 10 THEN 1 ELSE 0 END) as October,
SUM(CASE WHEN month_of_year = 11 THEN 1 ELSE 0 END) as November,
SUM(CASE WHEN month_of_year = 12 THEN 1 ELSE 0 END) as December
FROM datetest
INNER JOIN sys_calendar.calendar cal
ON cal.calendar_date BETWEEN start_date and end_date
GROUP BY record_id;
DROP TABLE datetest;
Because Quarter was mentioned in the question (I'm not sure how it relates here) there is also quarter_of_year and month_of_quarter available in the sys_calendar to slice and dice this even further.
Also, if you are on 16.00+ There is PIVOT functionality which may help get rid of the CASE statements here.

Answer 2

First join with the calendar to get all the dates within the range and get the number of days per each month (incl. full month, not mentioned in Start_Date and End_Date).
Then sum up each month in a column per Range.
create table SplitDateRange ( Range bigint, Start_Date date, End_Date date );
insert into SplitDateRange values ( 1, '2018-10-05', '2018-12-14' );
insert into SplitDateRange values ( 2, '2018-11-20', '2018-12-31' );
insert into SplitDateRange values ( 3, '2018-10-28', '2018-12-02' );
select
Range
, sum(case when mon = 10 then days else 0 end) as "Oct"
, sum(case when mon = 11 then days else 0 end) as "Nov"
, sum(case when mon = 12 then days else 0 end) as "Dec"
from (
select
Range
, extract(MONTH from C.calendar_date) as mon
, max(C.calendar_date) - min(calendar_date) +1 as days
from Sys_Calendar.CALENDAR as C
inner join SplitDateRange as DR
on C.calendar_date between DR.Start_Date and DR.End_Date
group by 1,2
) A
group by Range
order by Range
;

Answer 3

Different approach, avoids the cross join to the calendar by applying Teradata Expand On feature for creating time series. More text, but should be more efficient for larger tables/ranges:
SELECT record_id,
Sum(CASE WHEN mth = 10 THEN days_in_month ELSE 0 END) AS October,
Sum(CASE WHEN mth = 11 THEN days_in_month ELSE 0 END) AS November,
Sum(CASE WHEN mth = 12 THEN days_in_month ELSE 0 END) AS December
FROM
( -- this Derived Table simply avoids repeating then EXTRACT/INTERVAL calculations (can't be done directly in the nested Select)
SELECT record_id,
Extract(MONTH From Begin(expanded_pd)) AS mth,
Cast((INTERVAL( base_pd P_INTERSECT expanded_pd) DAY) AS INT) AS days_in_month
FROM
(
SELECT record_id,
PERIOD(start_date, end_date+1) AS base_pd,
expanded_pd
FROM datetest
-- creates one row per month
EXPAND ON base_pd AS expanded_pd BY ANCHOR PERIOD Month_Begin
) AS dt
) AS dt
GROUP BY 1