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Oracle11g温习-第十四章：约束( constraint )

2013年4月27日星期六

10:48

1、约束的功能

通过一些强制性商业规则，保证数据的完整性、一致性

2、约束的类别

1 ) not null 不允许为空

2 ) check 数值类要求 约束该列的值必须满足某种要求

3 ) unique 唯一

4 ) primary key ( not null + unique ) 非空唯一 只能有一个主键 唯一标示一行记录

5 ) foreign key ( reference ) 外键

【当进行dml操作的时候会检查当前约束是延迟还是非延迟的

如果是可延迟的约束只有提交的时候才会检查约束】

3、约束的状态

1 ) enable validate( 默认 ) ：【约束会立刻生效，并且新旧数据都要符合约束】

SCOTT @ prod > alter table emp1 enable validate constraint pk_emp1;

alter table emp1

ERROR at line 1:

ORA-02437: cannot validate ( SCOTT.PK_EMP1 ) - primary key violated

-----新旧记录都必须符合约束

2 ) enable novalidate ：【约束会立刻生效，只检查新的数据，已经存在的数据可以不符合约束( 注意对primary key 和unique，必须先建立非唯一性索引 )】

SCOTT @ prod > create table emp1 as select * from emp;

Table created.

SCOTT @ prod > select * from emp1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7369 SMITH CLERK 7902 17-DEC-80 800 20

7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30

7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30

7566 JONES MANAGER 7839 02-APR-81 2975 20

7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30

7698 BLAKE MANAGER 7839 01-MAY-81 2850 30

7782 CLARK MANAGER 7839 09-JUN-81 2450 10

7788 SCOTT ANALYST 7566 19-APR-87 3000 20

7839 KING PRESIDENT 17-NOV-81 5000 10

7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30

7876 ADAMS CLERK 7788 23-MAY-87 1100 20

7900 JAMES CLERK 7698 03-DEC-81 950 30

7902 FORD ANALYST 7566 03-DEC-81 3000 20

7934 MILLER CLERK 7782 23-JAN-82 1300 10

SCOTT @ prod > update emp1 set empno=7788 where ename='KING';

1 row updated.

SCOTT @ prod > select * from emp1 WHERE EMPNO=7788;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7788 SCOTT ANALYST 7566 19-APR-87 3000 20

7788 KING PRESIDENT 17-NOV-81 5000 10

添加primary key ，到enable novalidate

SCOTT @ prod > alter table emp1 add constraint pk_emp1 primary key ( empno ) enable novalidate; 新数据校验 旧的数据不校验

pk_emp1 primary key ( empno ) enable novalidate

ERROR at line 2:

ORA-02437: cannot validate ( SCOTT.PK_EMP1 ) - primary key violated

——原因：在建立primary key 它需要建立unique index

——在empno 上建立索引( 非唯一性索引 )

SCOTT @ prod > create index emp1_empno_ind on emp1( empno ) tablespace indexes;

Index created.

SCOTT @ prod > alter table emp1 add constraint

pk_emp1 primary key ( empno ) using index enable novalidate ;

Table altered.

——新的记录必须符合约束，旧的不检查

SCOTT @ prod > update emp1 set empno=7788 where ename='FORD';

update emp1 set empno=7788 where ename='FORD'

ERROR at line 1:

ORA-00001: unique constraint ( SCOTT.PK_EMP1 ) violated

SCOTT @ prod > desc user_constraints ;

SCOTT @ prod > select constraint_name,constraint_type,status ,validated from user_constraints where

Constraint_name=’’; 【检查约束状态】

3 ) disable validate：约束失效，但不能做DML操作

4 ) disable novalidate：约束失效，不检查任何数据( 等同于禁用约束 )

4、修正约束( 将违背约束的记录插入到exceptions表里 )

1 ) SCOTT @ prod > @?/rdbms/admin/utlexpt1.sql

SQL> Rem

SQL> Rem $Header: utlexpt1.sql 24-jun-99.07:59:18 echong Exp $

11:47:09 SQL> Rem

11:47:09 SQL> Rem utlexpt1.sql

11:47:09 SQL> Rem

11:47:09 SQL> Rem NAME

11:47:09 SQL> Rem utlexpt1.sql - <one-line expansion of the name>

11:47:09 SQL> Rem

11:47:09 SQL> Rem DESCRIPTION

11:47:09 SQL> Rem <short description of component this file declares/defines>

11:47:09 SQL> Rem

11:47:09 SQL> Rem NOTES

11:47:09 SQL> Rem <other useful comments, qualifications, etc.>

11:47:09 SQL> Rem

11:47:09 SQL> Rem MODIFIED ( MM/DD/YY )

11:47:09 SQL> Rem echong 06/24/99 - rename

11:47:09 SQL> Rem echong 06/05/98 - exceptions table with urowid type

11:47:09 SQL> Rem echong 06/05/98 - Created

11:47:09 SQL> Rem

11:47:09 SQL>

11:47:09 SQL> create table exceptions( row_id urowid,

11:47:09 2 owner varchar2( 30 ),

11:47:09 3 table_name varchar2( 30 ),

11:47:09 4 constraint varchar2( 30 ) );

Table created. EXCEPTIONS

SCOTT @ prod > select * from tab;

TNAME TABTYPE CLUSTERID

------------------------------ ------- ----------

DEPT TABLE

EMP TABLE

BONUS TABLE

SALGRADE TABLE

ADMIN_EXT_EMPLOYEES TABLE

EMPLOYEES TABLE

TEST TABLE

EMP1 TABLE

EXCEPTIONS TABLE

9 rows selected.

SCOTT @ prod > alter table emp1 enable validate constraint pk_emp1 exceptions into exceptions; 【把违背约束的数据插入expections 表】

alter table emp1

ERROR at line 1:

ORA-02437: cannot validate ( SCOTT.PK_EMP1 ) - primary key violated

---------把违背约束的记录插入到exceptions 表里

SCOTT @ prod > select * from exceptions;

ROW_ID OWNER TABLE_NAME CONSTRAINT

------------------------------ -------------------- ------------------------------ ------------------------------

AAAM0/AAEAAAAGcAAI SCOTT EMP1 PK_EMP1

AAAM0/AAEAAAAGcAAH SCOTT EMP1 PK_EMP1

SCOTT @ prod > delete from emp1 where rowid in ( select row_id from exceptions );

2 rows deleted.

SCOTT @ prod >alter table emp1 enable validate constraint pk_emp1;

Table altered.

5、延迟性约束deferrable( 约束只在提交事务时检查 ) 并且回滚事务

SCOTT @ prod > alter table dept1 add constraint pk_dept1 primary key ( deptno );

Table altered.

SCOTT @ prod > alter table emp1 add constraint fk_emp1 foreign key(deptno) references dept1(deptno) deferrable;

Table altered.

——deferrable 可延迟（默认是immediate ，非 deferr 延迟）

SCOTT @ prod >set constraint fk_emp1 deferred;

Constraint set.

---------将约束fk_emp1 进入延迟状态数据可以正常插入但是提交会报错

SCOTT @ prod > select * from emp1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7369 SMITH CLERK 7902 17-DEC-80 800 20

7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30

7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30

7566 JONES MANAGER 7839 02-APR-81 2975 20

7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30

7698 BLAKE MANAGER 7839 01-MAY-81 2850 30

7782 CLARK MANAGER 7839 09-JUN-81 2450 10

7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30

7876 ADAMS CLERK 7788 23-MAY-87 1100 20

7900 JAMES CLERK 7698 03-DEC-81 950 30

7902 FORD ANALYST 7566 03-DEC-81 3000 20

7934 MILLER CLERK 7782 23-JAN-82 1300 10

12 rows selected.

SCOTT @ prod > select * from dept1;

DEPTNO DNAME LOC

---------- -------------- -------------

10 ACCOUNTING NEW YORK

20 RESEARCH DALLAS

30 SALES CHICAGO

40 OPERATIONS BOSTON

SCOTT @ prod > update emp1 set deptno=50 where empno=7900;

1 row updated.

SCOTT @ prod > commit;

commit

ERROR at line 1:

【ORA-02091: transaction rolled back

ORA-02291: integrity constraint ( SCOTT.FK_EMP1 ) violated - parent key not found】

SCOTT @ prod > select * from emp1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7369 SMITH CLERK 7902 17-DEC-80 800 20

7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30

7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30

7566 JONES MANAGER 7839 02-APR-81 2975 20

7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30

7698 BLAKE MANAGER 7839 01-MAY-81 2850 30

7782 CLARK MANAGER 7839 09-JUN-81 2450 10

7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30

7876 ADAMS CLERK 7788 23-MAY-87 1100 20

7900 JAMES CLERK 7698 03-DEC-81 950 30

7902 FORD ANALYST 7566 03-DEC-81 3000 20

7934 MILLER CLERK 7782 23-JAN-82 1300 10

12 rows selected.

——【插入记录只在提交( commit ) 时检查】

Alter table emp modify ( empno varchar2(6) not null ) 非空约束

Alter table emp add constraint constraint_name unique ( empno ) 唯一约束

Alter table emp add constraint constraint_name check ( sal >5000 );

Dba_column_contents ; dba_constraints;

添加主键或是唯一约束的时候必须添加索引

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原文地址：https://www.cnblogs.com/iyoume2008/p/7526435.html