//用alert修改约束除了not null外,改变其它的约束都要加constraint关键字,比如 alert table table_1 add[modify] username not null; alert table table_1 add constraint pk_userid primary (userid); alert table table_1 add constraint fk_userid foreign key (userid) references user(userid); alert table table_1 add constraint unique_cardid unique(cardid); alert table table_1 add constraint chk_sex check(sex in('男','女')); //删除约束 alert table table_1 drop constraint chk_sex //删除主键约束 ,必须带上cascade alert table table_1 drop primary key userid cascade; //显示当前用户所有的约束信息 select constraint_name,constraint_type,status ,validated from user_contraints where table_name='表名' //显示约束列的信息 select column_name,position from user_cons_columns where constraint_name='约束名' //更改表名 rename old_tableName to new_tableName;