#1292 - Incorrect datetime value: '0000-00-00 00:00:00' for column... と出て update できない
update sample set sampledate = NULL WHERE CAST(sampledate AS CHAR(20)) = '0000-00-00 00:00:00';
とすればよい。
update sample set sampledate = NULL WHERE CAST(sampledate AS CHAR(20)) = '0000-00-00 00:00:00';
とすればよい。