Split records based on date in sql - sql

Question

ID EFF_DT END_DT
FLA1 2018-01-01 00:00:00 2019-12-31 00:00:00
FLA1 2020-01-01 00:00:00 9999-12-31 00:00:00
The above structure needs to be splited. And the split should be based on the date.
the output should have additional column as year
ID EFF_DT END_DT YEAR
FLA1 2018-01-01 00:00:00 2019-12-31 00:00:00 2019
FLA1 2020-01-01 00:00:00 2020-12-31 00:00:00 2020
FLA1 2021-01-01 00:00:00 9999-12-31 00:00:00 2021
I am using union for this purpose and it is generating duplicates. Any other approach / refine solution will work. Thanks in advance.

Answer 1

You can use a recursive sub-query factoring clause:
WITH split ( ID, EFF_DT, END_DT, MAX_DT ) AS (
SELECT id,
eff_dt,
LEAST(
ADD_MONTHS( TRUNC( SYSDATE, 'YY' ), 12 ) - INTERVAL '1' DAY,
end_dt
),
end_dt
FROM table_name
UNION ALL
SELECT id,
end_dt + INTERVAL '1' DAY,
max_dt,
max_dt
FROM split
WHERE end_dt < max_dt
)
SELECT id,
eff_dt,
end_dt
FROM split;
Which, for your sample data:
CREATE TABLE table_name ( ID, EFF_DT, END_DT ) AS
SELECT 'FLA1', DATE '2018-01-01', DATE '2019-12-31' FROM DUAL UNION ALL
SELECT 'FLA1', DATE '2020-01-01', DATE '9999-12-31' FROM DUAL;
Outputs:
ID | EFF_DT | END_DT
:--- | :------------------ | :------------------
FLA1 | 2018-01-01 00:00:00 | 2019-12-31 00:00:00
FLA1 | 2020-01-01 00:00:00 | 2020-12-31 00:00:00
FLA1 | 2021-01-01 00:00:00 | 9999-12-31 00:00:00
db<>fiddle here

Answer 2

If you want to generate all years of data, then:
with cte (id, eff_dt, end_dt, orig_end_dt)
select id, eff_dt, end_dt, end_dt
from t
union all
select cte.id, end_dt + interval '1' day,
least(orig_end_dte, trunc(end_dt, 'YYYY') + interval '1' year
from cte
where trunc(eff_dt, 'YYYY') < trunc(end_dt, 'YYYY')
)
select id, eff_dt, end_dt, to_char(end_dt, 'YYYY') as year
from cte;
Note: This produces a separate row for every year in the period.
If you want a limit on the year, then it would be something like this:
with cte (id, eff_dt, end_dt, orig_end_dt)
select id, eff_dt, end_dt, end_dt
from t
union all
select cte.id, end_dt + interval '1' day,
least(orig_end_dte, trunc(end_dt, 'YYYY') + interval '1' year
from cte
where trunc(eff_dt, 'YYYY') < least(trunc(end_dt, 'YYYY'), date '2021-01-01')
)
select id, eff_dt,
(case when end_dt = date '2021-12-31' then orig_end_dt else end_dt end),
to_char(end_dt, 'YYYY') as year
from cte;