Create time intervals based on values in one column / SQL Oracle - sql

Question

I need to create query that will return time intervals from table, that has attributes for (almost) every day.
The original table looks like the following:
Person | Date | Date_Type
-------|------------|----------
Sam | 01.06.2020 | Vacation
Sam | 02.06.2020 | Vacation
Sam | 03.06.2020 | Work
Sam | 04.06.2020 | Work
Sam | 05.06.2020 | Work
Frodo | 01.06.2020 | Work
Frodo | 02.06.2020 | Work
.....
And the desired should look like:
Person | Date_Interval | Date_Type
-------|-----------------------|----------
Sam | 01.06.2020-02.06.2020 | Vacation
Sam | 03.06.2020-05.06.2020 | Work
Frodo | 01.06.2020-02.06.2020 | Work
.....
Will be grateful for any idea :)

Answer 1

This reads like a gaps-and-island problem. Here is one approach:
select person, min(date) startdate, max(date) enddate, date_type
from (
select t.*,
row_number() over(partition by person order by date) rn1,
row_number() over(partition by person, date_type order by date) rn2
from mytable t
) t
group by person, date_type, rn1 - rn2
This also works if not all dates are contiguous (since you stated that you have almost all dates, I understood you don't have them all).

Answer 2

This is a type of gaps-and-islands problem.
To get adjacent days with the same date_type, you can subtract a sequence. It will be constant for adjacent days. Then you can aggregate:
select person, date_type, min(date), max(date)
from (select t.*,
row_number() over (partition by person, date_type
order by date) as seqnum
from t
) t
group by person, date_type, (date - seqnum);

Answer 3

One of the simplest methods is to use MATCH_RECOGNIZE to perform a row-by-row comparison and aggregation:
SELECT *
FROM table_name
MATCH_RECOGNIZE (
PARTITION BY Person
ORDER BY "DATE"
MEASURES
FIRST( "DATE" ) AS start_date,
LAST( "DATE") AS end_date,
FIRST( Date_Type ) AS date_type
ONE ROW PER MATCH
PATTERN ( successive_dates+ )
DEFINE
SUCCESSIVE_DATES AS (
FIRST( Date_Type ) = NEXT( Date_Type )
AND MAX( "DATE" ) + INTERVAL '1' DAY = NEXT( "DATE")
)
);
Which, for the sample data:
CREATE TABLE table_name ( Person, "DATE", Date_Type ) AS
SELECT 'Sam', DATE '2020-06-01', 'Vacation' FROM DUAL UNION ALL
SELECT 'Sam', DATE '2020-06-02', 'Vacation' FROM DUAL UNION ALL
SELECT 'Sam', DATE '2020-06-03', 'Work' FROM DUAL UNION ALL
SELECT 'Sam', DATE '2020-06-04', 'Work' FROM DUAL UNION ALL
SELECT 'Sam', DATE '2020-06-05', 'Work' FROM DUAL UNION ALL
SELECT 'Frodo', DATE '2020-06-01', 'Work' FROM DUAL UNION ALL
SELECT 'Frodo', DATE '2020-06-02', 'Work' FROM DUAL;
Outputs:
PERSON | START_DATE | END_DATE | DATE_TYPE
:----- | :------------------ | :------------------ | :--------
Frodo | 2020-06-01 00:00:00 | 2020-06-01 00:00:00 | Work
Sam | 2020-06-01 00:00:00 | 2020-06-01 00:00:00 | Vacation
Sam | 2020-06-03 00:00:00 | 2020-06-04 00:00:00 | Work
db<>fiddle here