SQL get consecutive starting and end date with specific period - mysql

Question

I have a hotel_availablities table something like this.
date
availability
2021-01-15
y
2021-01-16
y
2021-01-17
y
2021-01-18
n
2021-01-19
n
2021-01-20
y
2021-01-21
n
2021-01-22
y
2021-01-23
y
I wanted to get the results of possible available date range values where period of stay is 2 days.
date range
2021-01-15 : 2021-01-16
2021-01-16 : 2021-01-17
2021-01-22 : 2021-01-23
If period of stays was 3 days I would get results as below
date range
2021-01-15 : 2021-01-18
How can I achieve this result with sql?

Answer 1

This is a gaps and islands problem. Assuming you are using MySQL 8+, we can use the difference in row numbers method here:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY date) rn1,
ROW_NUMBER() OVER (PARTITION BY availability ORDER BY date) rn2
FROM yourTable
)
SELECT MIN(date) AS start_date, MAX(date) AS end_date, COUNT(*) AS cnt
FROM cte
WHERE availability = 'y'
GROUP BY rn1 - rn2
HAVING COUNT(*) >= 2; -- but change to COUNT(*) >= 3, e.g. for three days in a row
Demo
Note that my query does not give the exact output you expect, but maybe this would be enough for your requirement. If you wanted to break out each island larger than 2 days in terms of pairs of 2 days at a time, you might have to also bring in a calendar table here.

Answer 2

Assuming you have a row for each date, you can use a single window function -- and no aggregation. That window function is a count of 'y" in the current row and next n - 1 days:
select date, date + interval <n - 1> day
from (select t.*,
sum(availability = 'y') over (order by date
rows between current row and <n - 1> following
) as num_y
from t
) t
where num_y = <n>;

Answer 3

Through below query you can achieve that. First I have numbered the rows with row_number()
user lead() to get next consecutive dates. In lead second parameter is determining how many consecutive dates will be considered.
WITH t AS (
SELECT date ,ROW_NUMBER() OVER(ORDER BY date) rownumber
FROM hotel_availablities where availability='y'
),
t2 as (SELECT date StartDate ,lead(date ,1)over (partition by date_add(date ,INTERVAL -rownumber day)) EndDate
FROM t)
select concat(startdate,' - ',enddate)daterange from t2 where enddate is not null