MySQL 5.7

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CREATE TABLE table1 (
  column1 DATETIME(3),
  column2 DATETIME
);

INSERT INTO table1 (column1, column2) VALUES 
  ('2020-02-04 12:34:46.789', '2020-02-04 12:34:46.789')
SELECT column1, column2 FROM table1;

column1
column2

2020-02-04 12:34:46.789
2020-02-04 12:34:47

DESC table1;

Field
Type
Null
Key
Default
Extra

column1
datetime(3)
YES

null

column2
datetime
YES

null

SELECT CAST(column2 AS DATETIME(3)) FROM table1;

CAST(column2 AS DATETIME(3))

2020-02-04 12:34:47.000

SELECT NOW(3);

NOW(3)

2023-08-03 09:05:52.210