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CREATE TABLE test (t_from DATETIME, t_till DATETIME);
✓
hidden batch(es)
INSERT INTO test
VALUES
('2001-01-01','2001-01-03'),
('2001-01-05','2001-01-07'),
('2001-01-07','2001-01-09'),
('2001-01-11','2001-01-15'),
('2001-01-12','2001-01-14'),
('2001-01-17','2001-01-19'),
('2001-01-18','2001-01-20'),
('2001-01-19','2001-01-21');
✓
hidden batch(es)
select t_from, t_till
from ( select @start t_from, @start := t_from t_till, @weight needed, @weight := @weight + weight
from ( select t_from, 1 weight
from test
union all
select t_till, -1
from test
) x, (select @weight := 0, @start := 0) y
order by CAST(t_from AS DATE)
) z
where needed = 0 and t_from > 0 and t_from != t_till;
