coderisimo

сreate table tickets(id INT NULL,film_name VARCHAR(100) NULL, start_time DATETIME ,dur INT NULL	);

INSERT INTO tickets (id, film_name, start_time, dur)
VALUES 
  (1, 'f1', '2020-10-10 12:00:00', 60),
    (2, 'f2', '2020-10-10 11:30:00', 20),
    (3, 'f3', '2020-10-10 10:50:00', 90),
    (4, 'f4', '2020-10-10 11:10:00', 60),
    (5, 'f5', '2020-10-10 10:50:00', 120);


#-------------САМО РЕШЕНИЕ-------------------

SET @film_id := 1;  # здесь у нас ID фильма по которому проверяем интервалы
SET @startRange = (SELECT start_time FROM tickets WHERE id= @film_id)  ;
SET @endRange = (SELECT start_time + INTERVAL dur MINUTE FROM tickets WHERE id= @film_id);

select * from 
(select * , start_time + INTERVAL dur MINUTE as end_time from tickets) 
as table_with_end_time
WHERE
 (table_with_end_time.start_time >=  @startRange AND table_with_end_time.start_time  <=  @endRange)
OR(table_with_end_time.end_time >=  @startRange AND table_with_end_time.end_time  <=  @endRange )
OR(table_with_end_time.start_time <=  @startRange AND table_with_end_time.end_time >=  @endRange)

//f1, f2 - все поля  по которым ищем дубликаты
SELECT f1, f2, COUNT( f1) AS cnt
FROM table
GROUP BY f1, f2
HAVING (cnt > 1)