你看下你传入的字段是什么类型的，格式是什么
官方文档
https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html#function_last-day

mysql> SELECT LAST_DAY(‘2003-02-05’);
-> ‘2003-02-28’
mysql> SELECT LAST_DAY(‘2004-02-05’);
-> ‘2004-02-29’
mysql> SELECT LAST_DAY(‘2004-01-01 01:01:01’);
-> ‘2004-01-31’
mysql> SELECT LAST_DAY(‘2003-03-32’);
-> NULL