Search notes:

ORA-01821: date format not recognized

Fractional seconds

The following statement throws ORA-01821: date format not recognized (note the three f's with which the user tries to accommodate for the three fractional digits):
select
   to_timestamp('2025-01-13 07:16:14.353', 'yyyy-mm-dd hh24:mi:ss.fff')
from
   dual;
With only two f's, the query runs ok:
select
   to_timestamp('2025-01-13 07:16:14.353', 'yyyy-mm-dd hh24:mi:ss.ff')
from
   dual;

See also

to_char
Other Oracle error messages such as ORA-01830: date format picture ends before converting entire input string

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