MySQL 5.6

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select version();

version()

5.6.51

-- fractional seconds in DATETIME arrived in MySQL 5.6
create table ev (id int, at datetime(3));
insert into ev values (1,'2026-01-01 12:00:00.123'),(2,'2026-01-01 12:00:00.456');

Records: 2  Duplicates: 0  Warnings: 0

select id, at from ev order by at;

id
at

1
2026-01-01 12:00:00.123

2
2026-01-01 12:00:00.456