MySQL 8.0

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create table test (
    id MEDIUMINT NOT NULL AUTO_INCREMENT,
    worker_id int,
    dt_start date,
    dt_end date,
    PRIMARY KEY (id) );
insert into test (id, worker_id, dt_start, dt_end) values
    ('12', '20', '2014-05-02', '2014-07-08'),
    ('13', '20', '2017-01-14', '2017-01-31'),
    ('14', '20', '2017-04-18', '2099-01-01'),
    ('15', '20', '2017-11-06', '2017-11-06'),
    ('16', '20', '2017-11-06', '2017-12-07'),
    ('17', '20', '2019-12-02', '2020-05-31'),
    ('18', '20', '2020-06-01', '2020-07-31'),
    ('25', '29', '2014-11-24', '2017-02-11'),
    ('26', '42', '2016-01-22', '2016-05-05'),
    ('40', '71', '2016-12-01', '2017-05-31'),
    ('41', '71', '2017-06-01', '2020-12-21'),
    ('42', '71', '2020-07-17', '2020-08-02'),
    ('53', '380', '2017-02-15', '2017-07-31'),
    ('54', '380', '2017-09-04', '2017-12-23'),
    ('55', '380', '2017-12-27', '2018-12-22'),
    ('56', '380', '2019-05-15', '2019-09-15'),
    ('57', '380', '2020-03-23', '2099-01-01'),
    ('58', '380', '2020-09-28', '2022-09-30'),
    ('63', '391', '2013-07-23', '2013-11-30'),
    ('64', '391', '2014-06-16', '2014-12-16'),
    ('65', '391', '2014-11-21', '2015-01-20'),
    ('66', '391', '2015-04-01', '2015-04-15'),
    ('67', '391', '2015-06-10', '2015-06-22');
SELECT * FROM test;

Records: 23  Duplicates: 0  Warnings: 0

id	worker_id	dt_start	dt_end
12	20	2014-05-02	2014-07-08
13	20	2017-01-14	2017-01-31
14	20	2017-04-18	2099-01-01
15	20	2017-11-06	2017-11-06
16	20	2017-11-06	2017-12-07
17	20	2019-12-02	2020-05-31
18	20	2020-06-01	2020-07-31
25	29	2014-11-24	2017-02-11
26	42	2016-01-22	2016-05-05
40	71	2016-12-01	2017-05-31
41	71	2017-06-01	2020-12-21
42	71	2020-07-17	2020-08-02
53	380	2017-02-15	2017-07-31
54	380	2017-09-04	2017-12-23
55	380	2017-12-27	2018-12-22
56	380	2019-05-15	2019-09-15
57	380	2020-03-23	2099-01-01
58	380	2020-09-28	2022-09-30
63	391	2013-07-23	2013-11-30
64	391	2014-06-16	2014-12-16
65	391	2014-11-21	2015-01-20
66	391	2015-04-01	2015-04-15
67	391	2015-06-10	2015-06-22

id	worker_id	dt_start	dt_end	range_start	range_end
12	20	2014-05-02	2014-07-08	2014-05-02	2014-07-08
13	20	2017-01-14	2017-01-31	2017-01-14	2017-01-31
14	20	2017-04-18	2099-01-01	2017-04-18	2099-01-01
15	20	2017-11-06	2017-11-06	2017-04-18	2099-01-01
16	20	2017-11-06	2017-12-07	2017-04-18	2099-01-01
17	20	2019-12-02	2020-05-31	2017-04-18	2099-01-01
18	20	2020-06-01	2020-07-31	2017-04-18	2099-01-01
25	29	2014-11-24	2017-02-11	2014-11-24	2017-02-11
26	42	2016-01-22	2016-05-05	2016-01-22	2016-05-05
40	71	2016-12-01	2017-05-31	2016-12-01	2017-05-31
41	71	2017-06-01	2020-12-21	2017-06-01	2020-12-21
42	71	2020-07-17	2020-08-02	2017-06-01	2020-12-21
53	380	2017-02-15	2017-07-31	2017-02-15	2017-07-31
54	380	2017-09-04	2017-12-23	2017-09-04	2017-12-23
55	380	2017-12-27	2018-12-22	2017-12-27	2018-12-22
56	380	2019-05-15	2019-09-15	2019-05-15	2019-09-15
57	380	2020-03-23	2099-01-01	2020-03-23	2099-01-01
58	380	2020-09-28	2022-09-30	2020-03-23	2099-01-01
63	391	2013-07-23	2013-11-30	2013-07-23	2013-11-30
64	391	2014-06-16	2014-12-16	2014-06-16	2015-01-20
65	391	2014-11-21	2015-01-20	2014-06-16	2015-01-20
66	391	2015-04-01	2015-04-15	2015-04-01	2015-04-15
67	391	2015-06-10	2015-06-22	2015-06-10	2015-06-22