試驗環境：
1）數據庫版本：oracle 11.2.0.4
2）建表腳本：以scott的dept及emp表為基礎。
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-外鍵約束FK
主-外鍵約束指的是子表的某一字段的內容取值范圍必須由主表指定。
1）創建2張測試表：
create table f1 as select * from dept;
create table s1 as select * from emp;
說明：目前僅僅是復制了表結構及數據，未建立任何約束。
2）在未給f1.deptno創建主鍵或唯一約束，首選為s1.deptno創建外鍵：
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
結論：在子表中設置的與父表關聯的外鍵字段時，這個字段在父表中必須具有主鍵約束或唯一約束才可以設置成功。否則無法設置外鍵約束。
3)首先為F1.DEPTNO創建主鍵約束，然后再在S1.DEPTNO設置依賴於F1的外鍵，即可創建成功。
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）刪除F1的約束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
結論：若想刪除被外鍵依賴的主鍵信息時，需要首先刪除與其關聯的外鍵，然后再刪除主鍵：
SQL> alter table s1 drop constraint fk_deptno_s1;
Table altered.
SQL> alter table f1 drop constraint pk_f1;
Table altered.
5）首先為F1.DEPTNO創建唯一約束，然后再在S1.DEPTNO設置依賴於F1的外鍵，即可創建成功。
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）與步驟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）總結：外鍵依賴於父表字段的主鍵約束或唯一約束，有外鍵約束時，如果想刪除主鍵或唯一約束需要先刪除其外鍵約束。
8）針對於父表的delete或drop操作，如存在依賴關系需要首先處理子表數據，然后再處理父表數據。
9）針對於對父表的delete操作，外鍵設置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;
查詢現在F1和S1表的數據：
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.
刪除F1表中10部門數據：
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.
結論：在外鍵中使用on delete cascade時，刪除父表的數據時會同時刪除與父表數據相關聯的子表數據。
10）針對於對父表的delete操作，外鍵設置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;
查詢F1和S1現在數據：
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.
刪除F1表中10部門的數據：
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.
結論：在外鍵關聯中使用on delete set null時，刪除父表數據並不會同時刪除與之關聯的子表數據，而是將外鍵關聯字段自動修改成null。
11）外鍵管理存在時，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
刪除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
結論：在drop父表時，如果使用cascade constraint時，會刪除父表同時刪除子表的外鍵約束信息，但是不會刪除子表信息。
二、修改約束
1、為表add約束：
>語法：alter table table_name add constraint
創建測試表：
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
此時S1表沒有任何字段。
1）為表S1.EMP添加主鍵約束：
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）為表S1.SAL增加檢查約束：在表中add約束時首先要保證已有數據沒有違反約束。
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）增加外鍵約束：
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）增加唯一約束：
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）增加非空約束：不能通過alter table table_name add constraint命令添加，只能通過修改表的方式增加：
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、啟用/禁用約束
>禁用約束語法：alter table table_name disable constraint cons_name [cascade];
>啟用約束語法：alter table table_name enable constraint cons_name;
1）禁用表S1的約束
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）啟用表S1約束
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約束
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：此處因為PK_F1存在外鍵約束，所以禁止禁用PK_F1約束。
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：禁用父表帶有外鍵的約束時，可以采用cascade方式禁用約束，該方式同時也會禁用掉子表的外鍵約束。
3、刪除約束：
語法：alter table table_name drop constraint cons_name [cascade];
1）刪除S1中非外鍵約束
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）刪除F1表中的pk_f1約束
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：不允許刪除帶有外鍵約束的主表約束。
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刪除父表約束時，會同時刪除子表約束。
三、查看約束信息：
通過user_constraint和user_cons_columns字典表查詢約束信息，同時也以次字典表為基礎編寫約束日常監控腳本：
>CONSTRAINT_TYPE類型：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