MySQL 8.0

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CREATE TABLE sample_data (
  `concurrent_users` INTEGER,
  `concurrent_timestamp` VARCHAR(30),
  `concurrent_date` DATE
);

INSERT INTO sample_data
  (`concurrent_users`, `concurrent_timestamp`, `concurrent_date`)
VALUES
  ('3', '2020-06-24 07:20:00 UTC', '2020-06-24'),
  ('7', '2020-06-24 08:20:00 UTC', '2020-06-24'),
  ('8', '2020-07-05 06:20:00 UTC', '2020-07-05'),
  ('2', '2020-07-05 03:20:00 UTC', '2020-07-05');
select concurrent_timestamp, maxid 
from sample_data s INNER JOIN (select concurrent_date, max(concurrent_users) maxid
from sample_data
group by concurrent_date) s1 ON s.concurrent_users = s1.maxid; 


concurrent_timestamp
maxid


2020-06-24 08:20:00 UTC
7

2020-07-05 06:20:00 UTC
8