mysql> select now(3), from_unixtime(floor((unix_timestamp(now(3))+30)/60)*60) as nearest_minute; +-------------------------+---------------------+ | now(3) | nearest_minute | +-------------------------+---------------------+ | 2020-07-31 18:46:22.518 | 2020-07-31 18:46:00 | +-------------------------+---------------------+

Simplemente use CAST como DATETIME

 CREATE TABLE Table1 (`dt` datetime(6)) ; INSERT INTO Table1 (`dt`) VALUES ('2020-07-27 17:33:59.954'), ('2020-07-27 17:42:58.799') ;

 SELECT `dt` ,CAST(`dt` AS DATETIME) FROM Table1

dt | CAST(`dt` COMO FECHAHORA)
:-------------------------- | :-------------------------------------
2020-07-27 17:33:59.954000 | 2020-07-27 17:34:00   
2020-07-27 17:42:58.799000 | 2020-07-27 17:42:59   

db<>violín aquí

Aquí está la solución bastante insatisfactoria que se me ocurrió:

 CREATE FUNCTION timestamp_to_nearest_minute (t DATETIME) RETURNS DATETIME DETERMINISTIC RETURN CASE WHEN CAST(EXTRACT(MICROSECOND FROM t) AS DECIMAL(11,3)) / 1000.0 < 500 THEN DATE_SUB(t, INTERVAL CAST(EXTRACT(MICROSECOND FROM t) AS DECIMAL(11,3)) MICROSECOND) ELSE DATE_ADD(t, INTERVAL 1000000.0 - CAST(EXTRACT(MICROSECOND FROM t) AS DECIMAL(11,3)) MICROSECOND) END ;