oracle 约束[constraint]笔记

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 //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   constraintchk_sex//删除主键约束 ,必须带上cascadealert 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;

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