MySQL 5.5

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CREATE TABLE elbat
             (meta_key varchar(32),
              meta_value varchar(32));
INSERT INTO elbat
            (meta_key,
             meta_value)
            VALUES
('schedule_1_date', 	'2021/2/7'),
('schedule_1_lesson', 	'100'),
('schedule_2_date', 	'2020/12/30'),
('schedule_2_lesson', 	'105'),
('schedule_3_date', 	'2021/2/8'),
('schedule_3_lesson', 	'90'),
('schedule_4_date', 	'2021/5/10'),
('schedule_4_lesson', 	'91');

Records: 8  Duplicates: 0  Warnings: 0


SELECT t1.meta_key,
       t1.meta_value
       FROM elbat t1
            INNER JOIN (SELECT replace(replace(meta_key,
                                               'schedule_',
                                               ''),
                                       '_date',
                                       '') n
                               FROM elbat t2
                               WHERE t2.meta_key REGEXP '^schedule_[0-9]+_date$'
                                     AND t2.meta_value IN ('2021/2/7',
                                                           '2021/2/8')) n
                       ON t1.meta_key IN (concat('schedule_', n.n, '_date'),
                                          concat('schedule_', n.n, '_lesson'))


meta_key
meta_value


schedule_1_date
2021/2/7

schedule_1_lesson
100

schedule_3_date
2021/2/8

schedule_3_lesson
90

meta_key	meta_value
schedule_1_date	2021/2/7
schedule_1_lesson	100
schedule_3_date	2021/2/8
schedule_3_lesson	90