MySQL 8.0

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CREATE TABLE `tarif` (                  
  `tarif_id` int(11) NOT NULL AUTO_INCREMENT,
  `start_tarif` date NOT NULL,
  `end_tarif` date NOT NULL,
  `day_tarif` varchar(50) NOT NULL,
  PRIMARY KEY (`tarif_id`)
);
INSERT INTO `tarif` VALUES
  (1, '2019-02-01', '2019-02-10', '10'),
  (2, '2019-02-11', '2019-02-20', '20'),
  (3, '2019-02-21', '2019-02-28', '10'),
  (4, '2019-03-01', '2019-02-10', '15');
SELECT SUM(`day_tarif`) * COUNT(`tarif_id`) AS `sumCustom`, SUM(`day_tarif`) AS `sumDayTarif`, COUNT(`tarif_id`) AS `cntTarifID`
FROM `tarif` 
WHERE `end_tarif` >= '2019-02-05' AND `start_tarif` <= '2019-02-15'


sumCustom
sumDayTarif
cntTarifID


60
30
2


SELECT DATEDIFF(LEAST(`end_tarif`, '2019-02-15'), GREATEST(`start_tarif`, '2019-02-05')) + 1 AS sumDays, `day_tarif`
FROM `tarif` 
WHERE `end_tarif` >= '2019-02-05' AND `start_tarif` <= '2019-02-15'


sumDays
day_tarif


6
10

5
20


SELECT SUM((DATEDIFF(LEAST(`end_tarif`, '2019-02-15'), GREATEST(`start_tarif`, '2019-02-05')) + 1) * `day_tarif`) AS sumCustom
FROM `tarif` 
WHERE `end_tarif` >= '2019-02-05' AND `start_tarif` <= '2019-02-15'


sumCustom


160