Even UTC can be ambiguous when it comes to leap seconds. I don't know any major DBMS that can correctly store a leap second event in a standard datetime column.

Even UTC can be ambiguous when it comes to leap seconds. I don't know any major DBMS that can correctly store a leap second event in a standard datetime column. Perhaps the answer is to standardize on miliseconds since 1958 (19580101T000000Z) when TAI began.