Aggregate continuous ranges of dates - sql

Question

Let's say you have the following PostgreSQL sparse table listing reservation dates:
CREATE TABLE reserved_dates (
reserved_days_id SERIAL NOT NULL,
reserved_date DATE NOT NULL
);
INSERT INTO reserved_dates (reserved_date) VALUES
('2014-10-11'),
('2014-10-12'),
('2014-10-13'),
-- gap
('2014-10-15'),
('2014-10-16'),
-- gap
('2014-10-18'),
-- gap
('2014-10-20'),
('2014-10-21');
How do you aggregate those dates into continuous date ranges (ranges without gaps)? Such as:
start_date | end_date
------------+------------
2014-10-11 | 2014-10-13
2014-10-15 | 2014-10-16
2014-10-18 | 2014-10-18
2014-10-20 | 2014-10-21
This is what I came up with so far, but I can only get start_date this way:
WITH reserved_date_ranges AS (
SELECT reserved_date,
reserved_date
- LAG(reserved_date) OVER (ORDER BY reserved_date) AS difference
FROM reserved_dates
)
SELECT *
FROM reserved_date_ranges
WHERE difference > 1 OR difference IS NULL;

Answer 1

SELECT min(reserved_date) AS start_date
, max(reserved_date) AS end_date
FROM (
SELECT reserved_date
, reserved_date - row_number() OVER (ORDER BY reserved_date)::int AS grp
FROM reserved_dates
) sub
GROUP BY grp
ORDER BY grp;
Compute gap-less serial numbers in chronological order with the window function row_number(). Duplicate dates are not allowed. (I added a UNIQUE constraint in the fiddle.)
If your reserved_days_id happens to be gap-less and in chronological order, you can use that directly instead. But that's typically not the case.
Subtract that from reserved_date in each row (after converting to integer). Consecutive days end up with the same date value grp - which has no other purpose or meaning than to form groups.
Aggregate in the outer query. Voilá.
db<>fiddle here
Old sqlfiddle
Similar cases:
Rank based on sequence of dates
Group by repeating attribute