MySQL 8.0

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create table cl
(
    ID_client       int auto_increment
        primary key,
    service_time    time        not null,
    master          varchar(24) not null,
    `date`          date        not null,
    `time`          time        not null
);

INSERT INTO cl (service_time, master, `date`, `time`) VALUES 
('02:00:00', 'Lana', '2020-07-18', '14:30:00'),
('02:00:00', 'Lana', '2020-07-19', '14:30:00'),
('02:00:00', 'Lana', '2020-07-18', '15:00:00'),
('02:00:00', 'Lana', '2020-07-18', '16:45:00'),
('02:00:00', 'Alex', '2020-07-07', '20:00:00');

SELECT * FROM cl;


ID_client
service_time
master
date
time


1
02:00:00
Lana
2020-07-18
14:30:00

2
02:00:00
Lana
2020-07-19
14:30:00

3
02:00:00
Lana
2020-07-18
15:00:00

4
02:00:00
Lana
2020-07-18
16:45:00

5
02:00:00
Alex
2020-07-07
20:00:00


SELECT *,
       TIMESTAMP(`date`, `time`) start_datetime, 
       TIMESTAMP(CONCAT(`date`, ' ', `time`), service_time) final_datetime
FROM cl
ORDER BY 3,4,5;


ID_client
service_time
master
date
time
start_datetime
final_datetime


5
02:00:00
Alex
2020-07-07
20:00:00
2020-07-07 20:00:00
2020-07-07 22:00:00.000000

1
02:00:00
Lana
2020-07-18
14:30:00
2020-07-18 14:30:00
2020-07-18 16:30:00.000000

3
02:00:00
Lana
2020-07-18
15:00:00
2020-07-18 15:00:00
2020-07-18 17:00:00.000000

4
02:00:00
Lana
2020-07-18
16:45:00
2020-07-18 16:45:00
2020-07-18 18:45:00.000000

2
02:00:00
Lana
2020-07-19
14:30:00
2020-07-19 14:30:00
2020-07-19 16:30:00.000000


WITH
cte AS ( SELECT *,
                TIMESTAMP(`date`, `time`) start_datetime, 
                TIMESTAMP(CONCAT(`date`, ' ', `time`), service_time) final_datetime
         FROM cl )
SELECT DISTINCT t1.ID_client
FROM cte t1, cte t2
WHERE t1.start_datetime < t2.final_datetime
  AND t2.start_datetime < t1.final_datetime
  AND t1.master = t2.master
  AND t1.ID_client != t2.ID_client;


ID_client


3

4

1

ID_client	service_time	master	date	time
1	02:00:00	Lana	2020-07-18	14:30:00
2	02:00:00	Lana	2020-07-19	14:30:00
3	02:00:00	Lana	2020-07-18	15:00:00
4	02:00:00	Lana	2020-07-18	16:45:00
5	02:00:00	Alex	2020-07-07	20:00:00