CREATE TABLE IF NOT EXISTS `dobridol` (
`id` int(6) unsigned NOT NULL,
`dt` varchar(200) NOT NULL,
`p2` int(6) NOT NULL,
`p6` int(6) NOT NULL,
PRIMARY KEY (`id`)
) DEFAULT CHARSET=utf8;
INSERT INTO `dobridol` (`id`, `dt`, `p2`,`p6`) VALUES
('1', '2021-02-28 23:50:00', '100', '600'),
('2', '2021-02-28 23:55:00', '200', '700'),
('3', '2021-03-01 00:00:00', '300', '800'),
('4', '2021-03-01 00:05:00', '400', '900'),
('5', '2021-03-01 00:10:00', '400', '900'),
('6', '2021-03-01 00:15:00', '400', '900'),
('7', '2021-03-01 00:20:00', '500', '1000'),
('8', '2021-03-01 00:25:00', '600', '1100');
SELECT
p6,
id,
prev_val
FROM (
SELECT
dt,
p6,
id,
lag(p6) over (ORDER BY dt) AS prev_val
FROM dobridol
) tbl
WHERE dt BETWEEN '2021-03-01' AND '2021-03-30';