mysql 设置字段是否可以为null

//不允许为null
alter table table1 change id id int() not null;
//允许为null
alter table table1 change id id int() null;

//name_new允许为空
insert table1(id,transactor) values(,"world");

//transactor不允许为null
mysql> insert table1(id) values();
ERROR  (HY000): Field 'transactor' doesn't have a default value