MySQL 8.0

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create table t (date datetime,prince int);
insert into t values('2018-09-01 10:00:00', 123),
('2018-09-01 10:01:00' ,2568),
('2018-09-02 10:03:00', 25868),
('2018-09-02 10:10:00', 84213),
('2018-09-03 15:10:00', 58192),
('2018-09-03 10:16:00', 36)
;
select * from t t1
    where date in (select min(date) from t t2 
                         where date(t1.date)=date(t2.date)
                          group by date(date)
                      )


date
prince


2018-09-01 10:00:00
123

2018-09-02 10:03:00
25868

2018-09-03 10:16:00
36

date	prince
2018-09-01 10:00:00	123
2018-09-02 10:03:00	25868
2018-09-03 10:16:00	36