Oracle中如何建立約束,查詢約束和刪除約束(check約束,外來鍵和主鍵約束)
Oracle 建立主鍵,外來鍵, check約束的幾種方法:(write by RFH)
1. 在建立表時建立約束:
//新增主鍵約束
Create table userinfo (userid number(20)constraint pk_user primary key ,uname varchar(20));
Create table userinfo(userid number(20),unamevarchar(20),constraint pk_user primary key(userid);
//新增外來鍵約束
create table userinfo(useridnumber(20),deptid number(20) referencesdept(deptid));
create table userinfo(useridnumber(20),deptid number(20), constraint fk_dept foreign key(deptid)references dept(deptid));
//新增check約束
create table userinfo(useridnumber(20),age number(3) constraint ck_age check(age<100 and age>10));
create table userinfo(useridnumber(20),age number(3), constraint ck_age check(age<100 and age>10))
2. 假如你已經建表完成,而忘記新增約束,沒關係,可以單獨新增:
//新增主鍵約束:
alter table userinfo add constraintpk_user primary key(userid);
//新增外來鍵約束:
alter table userinfo add constraint fk_dept foreign key(deptid)references dept(deptid);
//新增check約束
alter table userinfo add constraint ck_age check(age<100 andage>10);
3對錶中約束的查詢:
Desc userinfo;
all_constraints 包含了表的約束資訊,但是會被刷屏
我們用user_constrains表來獲取當前使用者的約束:
select constraint_name,table_name,constraint_type from user_constraints;
如果我們要想看某個表的約束:
select constraint_name,table_name,constraint_type from user_constraints where table_name=’TABLENAME’;//注意表名要大寫
類似的,索引表USER_INDEXES,序列表USER_SEQUENCES,觸發器表USER_TRIGGERS,儲存過程表USER_PROCEDURES,當然還有USER_TABLES,VIEW_TABLES 等。有個驚人的發現,之前建的外來鍵會被新增到索引表中。他們中一般都有對應欄位table_name ,trigger_name等等。
4.我們已經可以自己建立和查詢約束,那麼如果想要刪掉無用的約束呢?
//刪除主鍵
alter table dept drop primary key;
或者
alter table userinfo drop constraint pk_user;
//刪除check約束
alter table userinfo drop constraint ck_age;
//刪除外來鍵約束
alter table userinfo drop constraint fk_dept;
用alter table語句:(僅供參考)
完整用法:
ALTER [IGNORE] TABLE tbl_name alter_specification [,alter_specification] ... alter_specification: table_option ...
| ADD [COLUMN]column_definition [FIRST
| AFTER col_name ]
| ADD [COLUMN](column_definition,...)
| ADD {INDEX|KEY} [index_name] [index_type](index_col_name,...)
| ADD [CONSTRAINT[symbol]] PRIMARY KEY [index_type] (index_col_name,...)
| ADD [CONSTRAINT[symbol]] UNIQUE [INDEX|KEY] [index_name] [index_type] (index_col_name,...)
| ADD [FULLTEXT|SPATIAL] [INDEX|KEY] [index_name] (index_col_name,...)
| ADD [CONSTRAINT[symbol]] FOREIGN KEY [index_name] (index_col_name,...) [reference_definition]
| ALTER [COLUMN]col_name {SET DEFAULT literal | DROP DEFAULT}
| CHANGE [COLUMN] old_col_name column_definition [FIRST|AFTERcol_name]
| MODIFY [COLUMN]column_definition [FIRST | AFTER col_name]
| DROP [COLUMN] col_name
| DROP PRIMARY KEY
| DROP {INDEX|KEY} index_name
| DROP FOREIGN KEYfk_symbol
| DISABLE KEYS | ENABLE KEYS | RENAME [TO] new_tbl_name
| ORDER BY col_name [, col_name] ...
| CONVERT TO CHARACTERSET charset_name [COLLATE collation_name]
| [DEFAULT] CHARACTERSET charset_name [COLLATE collation_name]
| DISCARD TABLESPACE
| IMPORT TABLESPACE