Date split-up based on Fiscal Year - sql

Question

Given a From Date, To Date and a Fiscal Year system, I want to get all the split-up duration within the
given From & To Date based on the Fiscal Year system. Explained below with examples:
Example 1:
Fiscal Year system: Apr to Mar
From Date: Jan-05-2008
To Date: May-15-2008
Based on Fiscal Year system, duration should be splitted into:
Jan-05-2008 to Mar-31-2008
Apr-01-2008 to May-15-2008
Example 2:
Fiscal Year system: Apr to Mar
From Date: Jan-17-2008
To Date: May-20-2009
Based on Fiscal Year system, duration should be splitted into:
Jan-17-2008 to Mar-31-2008
Apr-01-2008 to Mar-31-2009
Apr-01-2009 to May-20-2009
Am looking for approach/algorithm to solve this in PostgreSQL 8.2.
Regards,
Gnanam

Answer 1

I actually favor Andomar's solution (with the addition of a processes that automatically fills the Periods table), but for fun here's a solution that doesn't require it.
CREATE TABLE your_table (start_date date, end_date date);
INSERT INTO your_table VALUES ('Jan-17-2008', 'May-20-2009');
SELECT
GREATEST(start_date, ('04-01-'||series.year)::date) AS year_start,
LEAST(end_date, ('03-31-'||series.year + 1)::date) AS year_end
FROM
(SELECT
start_date,
end_date,
generate_series(
date_part('year', your_table.start_date - INTERVAL '3 months')::int,
date_part('year', your_table.end_date - INTERVAL '3 months')::int)
FROM your_table) AS series(start_date, end_date, year)
ORDER BY
start_date;

Answer 2

You could create a table containing the start and end of all fiscal years, f.e.
Periods (PeriodStartDt, PeriodEndDt)
Then you can join the tables together if they at least partly overlap. Use a case statement to select the end of the period or the end of the row, depending on which is later. For example (not tested):
select case when yt.StartDt < p.PeriodStartDt then p.PeriodStartDt
else yt.StartDt
end as SplitStart
, case when yt.EndDt > p.PeriodEndDt then p.PeriodEndDt
else yt.EndDt
end as SplitEnd
, yt.*
from YourTable yt
inner join Periods p
on yt.StartDt < p.PeriodEndDate
and yt.EndDt >= p.PeriodStartDate

Answer 3

CREATE TABLE your_table (start_date date, end_date date);
INSERT INTO your_table VALUES (CONVERT (date, GETDATE()),CONVERT (date, DATEADD(year, -1, GETDATE())) );
WITH mycte AS
(
SELECT 1 as id
UNION ALL
SELECT id + 1
FROM mycte
WHERE id + 1 < = 12
),
cte_distribution as
(
SELECT *,
DATEPART (month,DATEADD(month, mycte.id - 1, your_table.start_date)) as month_number ,
DATEPART (YEAR,DATEADD(month, mycte.id - 1, your_table.start_date)) as cal_year,
12000/12 as cash
FROM your_table
CROSS JOIN mycte
)
select
*,
(CASE WHEN month_number between 1 and 3 THEN '1st quarter' WHEN month_number between 4 and 6 THEN '2nd quarter' WHEN month_number between 7 and 9 THEN '3rd quarter' WHEN month_number between 9 and 12 THEN '4th quarter' END) as Quarter,
CASE WHEN month_number between 1 and 6 THEN CAST(CAST((cal_year - 1) as CHAR(4)) + '-' + CAST(cal_year as CHAR(4)) AS CHAR(9)) WHEN month_number between 6 and 12 THEN CAST(CAST((cal_year) as CHAR(4)) + '-' + CAST((cal_year + 1) as CHAR(4)) AS CHAR(9)) ELSE NULL END as fin_year
from cte_distribution;