Oracle开发之主-外键约束FK及约束的修改-白红宇

Oracle开发之主-外键约束FK及约束的修改

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发布时间：2019-06-14

本文共 16564 字，大约阅读时间需要 55 分钟。

试验环境：

1）数据库版本：oracle 11.2.0.4

2）建表脚本：以scott的dept及emp表为基础。

父表：dept

-- Create table

create table DEPT

(

DEPTNO NUMBER(2) not null,

DNAME VARCHAR2(14),

LOC VARCHAR2(13)

)

-- Create/Recreate primary, unique and foreign key constraints

alter table DEPT

add constraint PK_DEPT primary key (DEPTNO)

using index;

子表emp：

-- Create table

create table EMP

(

EMPNO NUMBER(4) not null,

ENAME VARCHAR2(10),

JOB VARCHAR2(9),

MGR NUMBER(4),

HIREDATE DATE,

SAL NUMBER(7,2),

COMM NUMBER(7,2),

DEPTNO NUMBER(2)

)

-- Create/Recreate primary, unique and foreign key constraints

alter table EMP

add constraint PK_EMP primary key (EMPNO)

using index ;

alter table EMP

add constraint FK_DEPTNO foreign key (DEPTNO)

references DEPT (DEPTNO);

一、主-外键约束FK

主-外键约束指的是子表的某一字段的内容取值范围必须由主表指定。

1）创建2张测试表：

create table f1 as select * from dept;

create table s1 as select * from emp;

说明：目前仅仅是复制了表结构及数据，未建立任何约束。

2）在未给f1.deptno创建主键或唯一约束，首选为s1.deptno创建外键：

SQL> alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO);

alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO)

ERROR at line 1:

ORA-02270: no matching unique or primary key for this column-list

结论：在子表中设置的与父表关联的外键字段时，这个字段在父表中必须具有主键约束或唯一约束才可以设置成功。否则无法设置外键约束。

3)首先为F1.DEPTNO创建主键约束，然后再在S1.DEPTNO设置依赖于F1的外键，即可创建成功。

SQL> alter table F1 add constraint PK_F1 primary key (DEPTNO);

Table altered.

SQL> alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO);

Table altered.

4）删除F1的约束pk_f1：

SQL> alter table f1 drop constraint pk_f1;

alter table f1 drop constraint pk_f1

ERROR at line 1:

ORA-02273: this unique/primary key is referenced by some foreign keys

结论：若想删除被外键依赖的主键信息时，需要首先删除与其关联的外键，然后再删除主键：

SQL> alter table s1 drop constraint fk_deptno_s1;

Table altered.

SQL> alter table f1 drop constraint pk_f1;

Table altered.

5）首先为F1.DEPTNO创建唯一约束，然后再在S1.DEPTNO设置依赖于F1的外键，即可创建成功。

SQL> alter table F1 add constraint UK_F1 unique(deptno);

Table altered.

SQL> alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO);

Table altered.

6）与步骤4相同：

SQL> alter table f1 drop constraint uk_f1;

alter table f1 drop constraint uk_f1

ERROR at line 1:

ORA-02273: this unique/primary key is referenced by some foreign keys

7）总结：外键依赖于父表字段的主键约束或唯一约束，有外键约束时，如果想删除主键或唯一约束需要先删除其外键约束。

8）针对于父表的delete或drop操作，如存在依赖关系需要首先处理子表数据，然后再处理父表数据。

9）针对于对父表的delete操作，外键设置on delete cascade：

create table f1 as select * from dept;

create table s1 as select * from emp;

alter table F1 add constraint PK_F1 primary key (DEPTNO)

alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO) on delete cascade;

查询现在F1和S1表的数据：

SQL> select * from f1;

DEPTNO DNAME LOC

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

10 ACCOUNTING NEW YORK

20 RESEARCH DALLAS

30 SALES CHICAGO

40 OPERATIONS BOSTON

SQL> select * from s1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

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

7369 SMITH CLERK 7902 1980/12/17 00:00:00 800 20

7499 ALLEN SALESMAN 7698 1981/02/20 00:00:00 1600 300 30

7521 WARD SALESMAN 7698 1981/02/22 00:00:00 1250 500 30

7566 JONES MANAGER 7839 1981/04/02 00:00:00 2975 20

7654 MARTIN SALESMAN 7698 1981/09/28 00:00:00 1250 1400 30

7698 BLAKE MANAGER 7839 1981/05/01 00:00:00 2850 30

7782 CLARK MANAGER 7839 1981/06/09 00:00:00 2450 10

7788 SCOTT ANALYST 7566 1987/04/19 00:00:00 3000 20

7839 KING PRESIDENT 1981/11/17 00:00:00 5000 10

7844 TURNER SALESMAN 7698 1981/09/08 00:00:00 1500 0 30

7876 ADAMS CLERK 7788 1987/05/23 00:00:00 1100 20

7900 JAMES CLERK 7698 1981/12/03 00:00:00 950 30

7902 FORD ANALYST 7566 1981/12/03 00:00:00 3000 20

7934 MILLER CLERK 7782 1982/01/23 00:00:00 1300 10

14 rows selected.

删除F1表中10部门数据：

SQL> delete from f1 where deptno=10;

1 row deleted.

SQL> select * from f1;

DEPTNO DNAME LOC

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

20 RESEARCH DALLAS

30 SALES CHICAGO

40 OPERATIONS BOSTON

SQL> select * from s1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

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

7369 SMITH CLERK 7902 1980/12/17 00:00:00 800 20

7499 ALLEN SALESMAN 7698 1981/02/20 00:00:00 1600 300 30

7521 WARD SALESMAN 7698 1981/02/22 00:00:00 1250 500 30

7566 JONES MANAGER 7839 1981/04/02 00:00:00 2975 20

7654 MARTIN SALESMAN 7698 1981/09/28 00:00:00 1250 1400 30

7698 BLAKE MANAGER 7839 1981/05/01 00:00:00 2850 30

7788 SCOTT ANALYST 7566 1987/04/19 00:00:00 3000 20

7844 TURNER SALESMAN 7698 1981/09/08 00:00:00 1500 0 30

7876 ADAMS CLERK 7788 1987/05/23 00:00:00 1100 20

7900 JAMES CLERK 7698 1981/12/03 00:00:00 950 30

7902 FORD ANALYST 7566 1981/12/03 00:00:00 3000 20

11 rows selected.

SQL> commit;

Commit complete.

结论：在外键中使用on delete cascade时，删除父表的数据时会同时删除与父表数据相关联的子表数据。

10）针对于对父表的delete操作，外键设置on delete set null：

create table f1 as select * from dept;

create table s1 as select * from emp;

alter table F1 add constraint PK_F1 primary key (DEPTNO);

alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO) on delete set null;

查询F1和S1现在数据：

SQL> select * from f1;

DEPTNO DNAME LOC

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

10 ACCOUNTING NEW YORK

20 RESEARCH DALLAS

30 SALES CHICAGO

40 OPERATIONS BOSTON

SQL> select * from s1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

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

7369 SMITH CLERK 7902 1980/12/17 00:00:00 800 20

7499 ALLEN SALESMAN 7698 1981/02/20 00:00:00 1600 300 30

7521 WARD SALESMAN 7698 1981/02/22 00:00:00 1250 500 30

7566 JONES MANAGER 7839 1981/04/02 00:00:00 2975 20

7654 MARTIN SALESMAN 7698 1981/09/28 00:00:00 1250 1400 30

7698 BLAKE MANAGER 7839 1981/05/01 00:00:00 2850 30

7782 CLARK MANAGER 7839 1981/06/09 00:00:00 2450 10

7788 SCOTT ANALYST 7566 1987/04/19 00:00:00 3000 20

7839 KING PRESIDENT 1981/11/17 00:00:00 5000 10

7844 TURNER SALESMAN 7698 1981/09/08 00:00:00 1500 0 30

7876 ADAMS CLERK 7788 1987/05/23 00:00:00 1100 20

7900 JAMES CLERK 7698 1981/12/03 00:00:00 950 30

7902 FORD ANALYST 7566 1981/12/03 00:00:00 3000 20

7934 MILLER CLERK 7782 1982/01/23 00:00:00 1300 10

14 rows selected.

删除F1表中10部门的数据：

SQL> delete from f1 where deptno=10;

1 row deleted.

SQL> select * from f1;

DEPTNO DNAME LOC

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

20 RESEARCH DALLAS

30 SALES CHICAGO

40 OPERATIONS BOSTON

SQL> select * from s1;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

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

7369 SMITH CLERK 7902 1980/12/17 00:00:00 800 20

7499 ALLEN SALESMAN 7698 1981/02/20 00:00:00 1600 300 30

7521 WARD SALESMAN 7698 1981/02/22 00:00:00 1250 500 30

7566 JONES MANAGER 7839 1981/04/02 00:00:00 2975 20

7654 MARTIN SALESMAN 7698 1981/09/28 00:00:00 1250 1400 30

7698 BLAKE MANAGER 7839 1981/05/01 00:00:00 2850 30

7782 CLARK MANAGER 7839 1981/06/09 00:00:00 2450

7788 SCOTT ANALYST 7566 1987/04/19 00:00:00 3000 20

7839 KING PRESIDENT 1981/11/17 00:00:00 5000

7844 TURNER SALESMAN 7698 1981/09/08 00:00:00 1500 0 30

7876 ADAMS CLERK 7788 1987/05/23 00:00:00 1100 20

7900 JAMES CLERK 7698 1981/12/03 00:00:00 950 30

7902 FORD ANALYST 7566 1981/12/03 00:00:00 3000 20

7934 MILLER CLERK 7782 1982/01/23 00:00:00 1300

14 rows selected.

SQL> commit;

Commit complete.

结论：在外键关联中使用on delete set null时，删除父表数据并不会同时删除与之关联的子表数据，而是将外键关联字段自动修改成null。

11）外键管理存在时，drop父表操作：

create table f1 as select * from dept;

create table s1 as select * from emp;

alter table F1 add constraint PK_F1 primary key (DEPTNO);

alter table S1 add constraint FK_DEPTNO_S1 foreign key (DEPTNO) references F1 (DEPTNO);

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1','F1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT

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

F1 PK_F1 P

S1 FK_DEPTNO_S1 R

删除F1表：

SQL> drop table F1;

drop table F1

ERROR at line 1:

ORA-02449: unique/primary keys in table referenced by foreign keys

SQL> drop table f1 cascade constraint;

Table dropped.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1','F1');

no rows selected

SQL> select * from tab where tname='S1';

TNAME TABTYPE CLUSTERID

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

S1 TABLE

结论：在drop父表时，如果使用cascade constraint时，会删除父表同时删除子表的外键约束信息，但是不会删除子表信息。

二、修改约束

1、为表add约束：

>语法：alter table table_name add constraint

创建测试表：

create table f1 as select * from dept;

create table s1 as select * from emp;

alter table F1 add constraint PK_F1 primary key (DEPTNO);

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1');

no rows selected

此时S1表没有任何字段。

1）为表S1.EMP添加主键约束：

SQL> alter table s1 add constraint pk_s1 primary key (empno);

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT

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

S1 PK_S1 P

2）为表S1.SAL增加检查约束：在表中add约束时首先要保证已有数据没有违反约束。

SQL> alter table s1 add constraint ck_s1 check(sal > 100);

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT

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

S1 CK_S1 C

S1 PK_S1 P

3）增加外键约束：

SQL> alter table s1 add constraint fk_s1 foreign key(deptno) references f1(deptno);

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT

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

S1 CK_S1 C

S1 FK_S1 R

S1 PK_S1 P

4）增加唯一约束：

SQL> alter table s1 add constraint uk_s1 unique(ename);

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT

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

S1 CK_S1 C

S1 FK_S1 R

S1 UK_S1 U

S1 PK_S1 P

5）增加非空约束：不能通过alter table table_name add constraint命令添加，只能通过修改表的方式增加：

SQL> alter table s1 modify(SAL NUMBER(7,2) not null);

Table altered.

create table S1

(

EMPNO NUMBER(4) not null,

ENAME VARCHAR2(10),

JOB VARCHAR2(9),

MGR NUMBER(4),

HIREDATE DATE,

SAL NUMBER(7,2) not null,

COMM NUMBER(7,2),

DEPTNO NUMBER(2)

)

2、启用/禁用约束

>禁用约束语法：alter table table_name disable constraint cons_name [cascade];

>启用约束语法：alter table table_name enable constraint cons_name;

1）禁用表S1的约束

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C ENABLED

S1 FK_S1 R ENABLED

S1 UK_S1 U ENABLED

S1 PK_S1 P ENABLED

SQL> ALTER TABLE S1 DISABLE CONSTRAINT CK_S1;

Table altered.

SQL> ALTER TABLE S1 DISABLE CONSTRAINT UK_S1;

Table altered.

SQL> ALTER TABLE S1 DISABLE CONSTRAINT PK_S1;

Table altered.

SQL> ALTER TABLE S1 DISABLE CONSTRAINT FK_S1;

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C DISABLED

S1 FK_S1 R DISABLED

S1 UK_S1 U DISABLED

S1 PK_S1 P DISABLED

2）启用表S1约束

SQL> ALTER TABLE S1 ENABLE CONSTRAINT PK_S1;

Table altered.

SQL> ALTER TABLE S1 ENABLE CONSTRAINT CK_S1;

Table altered.

SQL> ALTER TABLE S1 ENABLE CONSTRAINT UK_S1;

Table altered.

SQL> ALTER TABLE S1 ENABLE CONSTRAINT FK_S1;

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C ENABLED

S1 FK_S1 R ENABLED

S1 UK_S1 U ENABLED

S1 PK_S1 P ENABLED

3）禁用F1表上的pk_f1约束

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C ENABLED

S1 FK_S1 R ENABLED

S1 UK_S1 U ENABLED

S1 PK_S1 P ENABLED

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('F1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

F1 PK_F1 P ENABLED

SQL> ALTER TABLE F1 DISABLE CONSTRAINT PK_F1;

ALTER TABLE F1 DISABLE CONSTRAINT PK_F1

ERROR at line 1:

ORA-02297: cannot disable constraint (SCOTT.PK_F1) - dependencies exist

注意：此处因为PK_F1存在外键约束，所以禁止禁用PK_F1约束。

SQL> ALTER TABLE F1 DISABLE CONSTRAINT PK_F1 CASCADE;

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('F1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

F1 PK_F1 P DISABLED

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C ENABLED

S1 FK_S1 R DISABLED

S1 UK_S1 U ENABLED

S1 PK_S1 P ENABLED

注意：禁用父表带有外键的约束时，可以采用cascade方式禁用约束，该方式同时也会禁用掉子表的外键约束。

3、删除约束：

语法：alter table table_name drop constraint cons_name [cascade];

1）删除S1中非外键约束

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 CK_S1 C ENABLED

S1 FK_S1 R ENABLED

S1 UK_S1 U ENABLED

S1 PK_S1 P ENABLED

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('F1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

F1 PK_F1 P ENABLED

SQL> ALTER TABLE S1 DROP CONSTRAINT CK_S1;

Table altered.

SQL> ALTER TABLE S1 DROP CONSTRAINT UK_S1;

Table altered.

SQL> ALTER TABLE S1 DROP CONSTRAINT PK_S1;

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 FK_S1 R ENABLED

S1 SYS_C0019909 C ENABLED

2）删除F1表中的pk_f1约束

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

S1 FK_S1 R ENABLED

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('F1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

F1 PK_F1 P ENABLED

SQL> ALTER TABLE F1 DROP CONSTRAINT PK_F1;

ALTER TABLE F1 DROP CONSTRAINT PK_F1

ERROR at line 1:

ORA-02273: this unique/primary key is referenced by some foreign keys

注意：不允许删除带有外键约束的主表约束。

SQL> ALTER TABLE F1 DROP CONSTRAINT PK_F1 CASCADE;

Table altered.

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('F1');

no rows selected

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('S1');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

no rows selected

注意：cascade删除父表约束时，会同时删除子表约束。

三、查看约束信息：

通过user_constraint和user_cons_columns字典表查询约束信息，同时也以次字典表为基础编写约束日常监控脚本：

>CONSTRAINT_TYPE类型：P、R、C、C（not null）、Q

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('EMP');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

EMP PK_EMP P ENABLED

EMP FK_DEPTNO R ENABLED

SQL> select TABLE_NAME,CONSTRAINT_NAME,CONSTRAINT_TYPE,STATUS from user_constraints where table_name in ('DEPT');

TABLE_NAME CONSTRAINT_NAME CONSTRAINT STATUS

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

DEPT PK_DEPT P ENABLED

转载于:https://www.cnblogs.com/wcwen1990/p/6660430.html

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