SQL - Select date ranges without overlapping - sql

Question

I have the following table (Oracle database):
ID
valid_from
valid_to
1
01.01.22
28.02.22
1
01.03.22
30.06.22
1
01.07.22
31.12.22
1
01.01.23
null
2
01.01.22
31.03.22
2
01.04.22
null
How do I best extract now all date ranges without overlaps over both IDs? The final result set should look like:
valid_from
valid_to
01.01.22
28.02.22
01.03.22
31.03.22
01.04.22
30.06.22
01.07.23
31.12.22
01.01.23
null
Null stands for max_date (PL / SQL Oracle Max Date).
Moreover, I should only select the values valid for the current year (let's assume we are already in 2022).
Thanks for your help in advance!

Answer 1

You can apply next select statement:
with
-- main table
t1 AS (SELECT w, q1, q2, to_date(q1,'dd.mm.yy') q1d, to_date(q2,'dd.mm.yy') q2d FROM www)
-- custom year in YYYY format
, t0 AS (SELECT '2022' y FROM dual)
-- join and order dates FROM - TO
, t2 AS (SELECT t1.q1, t1.q1d, s2.q2, s2.q2d
FROM t1
LEFT JOIN t1 s2 on t1.q1d <= s2.q2d
ORDER BY t1.q1d, s2.q2d)
-- mark the first each new row-pair by row_number()
, t3 AS (SELECT t2.*,
row_number() OVER (PARTITION BY t2.q1d ORDER BY t2.q1d ) r
FROM t2 )
-- join custom year value and select desired rows based on that value
SELECT q1, q2 FROM t3
JOIN t0 on 1=1
WHERE r = 1
-- for the custom year
AND t0.y <= to_char(q1d, 'yyyy')
ORDER BY q1d;
Demo
In my table-example dates are presented in varchar2 datatype and in dd.mm.yy date format. In case if your table fields have datatype date, then you don't need to implement function to_date() for those 2 fields.
Used table sample:
create table www (w integer, q1 varchar2(30), q2 varchar2(30));
insert into www values (1, '01.01.22', '28.02.22');
insert into www values (1, '01.03.22', '30.06.22');
insert into www values (1, '01.07.22', '31.12.22');
insert into www values (1, '01.01.23', '');
insert into www values (2, '01.01.22', '31.03.22');
insert into www values (2, '01.04.22', '');
If your table sample has more rows which are have null value in the field valid_to and the dates in valid_from are not in any range, let's say:
insert into www values (1, '01.01.24', '');
then previous solution will produce more rows in the end with null value.
In this case you can use that more complex solution:
...
-- join custom year value and select desired rows based on that value
, t4 as (SELECT q1, q2, q1d FROM t3
JOIN t0 on 1=1
WHERE r = 1 AND
-- for the custom year
t0.y <= to_char(q1d, 'yyyy')
ORDER BY q1d)
-- filter non-nullable rows
, t5 as ( SELECT q1, q2 FROM t4 WHERE Q2 IS NOT NULL )
-- max date from rows where Q2 field has null value
, t6 as ( SELECT to_char(MAX(Q1D),'dd.mm.yy') q1, q2
FROM t4
WHERE Q2 IS NULL
GROUP BY q2)
-- append rows with max date
SELECT * FROM t5
UNION ALL
SELECT * FROM t6;
Demo