今天处理了一个由于约束插入数据失败的问题，处理时感到有些吃力，三天不练手生啊。在这里回忆一下。
Oracle数据库Constraint约束的四对属性：Deferrable/not deferrable, Deferred/immediate, enable/disable, validate/novalidate。
准备一下环境：
SQL> create table empx as select * from emp;
SQL> create table deptx as select * from dept;
SQL> alter table empx add constraint pk_empx primary key(empno);
SQL> alter table deptx add constraint pk_deptx primary key(deptno);
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno);
SQL> select * from deptx;
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12DEPTNO DNAME LOC ---------- ------------------------------------------ --------------------------------------- 10 ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON
SQL> select * from empx;
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83EMPNO 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 14 rows selected.
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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18CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ------------------------ ---------------- ------------------------ ---------------- ---------------- ------------ PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50);
insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50)
*
ERROR at line 1:
ORA-02291: integrity constraint (SCOTT.FK_DEPTX) violated - parent key not found
这里通过emp和dept表创建了两张表empx和deptx,并在empx表上创建了外键约束fk_deptx。
1.Deferrable,not deferrable(default value)
1)这对属性是定义是否可以延时验证,deferrable是指作验证时机,如果在commit的时check为deferrable,否则为immediate .只有在设置Deferrable才可以设置另一属性Deferred,immediate.
2)这对属性是在创建的constraint的时候定义的,不能被修改.
notice:如果建立了Deferrable的uk或pk,只会建立相应的nonuniquce index,而不会建立uniquce index
SQL> alter table empx drop constraint fk_deptx;
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) deferrable;
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ------------------------ ---------------- ------------------------ ---------------- ---------------- ------------ PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED DEFERRABLE IMMEDIATE VALIDATED
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50);
insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50)
*
ERROR at line 1:
ORA-02291: integrity constraint (SCOTT.FK_DEPTX) violated - parent key not found
在会话级设置：
SQL> set constraint FK_DEPTX deferred;
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- --------------------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED DEFERRABLE IMMEDIATE VALIDATED
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50);
1 row created.
SQL> commit;
commit
*
ERROR at line 1:
ORA-02091: transaction rolled back
ORA-02291: integrity constraint (SCOTT.FK_DEPTX) violated - parent key not found
单独deferrable的含义就是是否允许约束检查延后进行。单独设置deferrable为deferrable之后，约束检查延后是不可以直接使用的，要配合deferred参数，如果该参数是immediate，那么约束还是在DML的时候进行应用。如果deferred参数设置为deferred，约束就是在事务commit提交的时候应用，出现错误就连带回滚rollback整个事务。
2.Deferred,immediate(default value)
deferred属性是配合deferrable属性使用的。当deferrable设置为deferrable之后，可以通过set constraints在会话级进行deferred属性的设置，来确定约束应用时点。
定义约束是使用initially关键字来确定约束的deferred属性取值。
SQL> alter table empx drop constraint fk_deptx;
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) deferrable initially deferred;
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- --------------------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED DEFERRABLE DEFERRED VALIDATED
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50);
1 row created.
SQL> commit;
commit
*
ERROR at line 1:
ORA-02091: transaction rolled back
ORA-02291: integrity constraint (SCOTT.FK_DEPTX) violated - parent key not found
可以通过创建contraint时指定Deferred值，也可以通过会话级别的语句SET CONSTRAINT(s)来设置（如上面的set constraint FK_DEPTX deferred）。
当属性DEFERRABLE和DEFERRED的值分别为DEFERRABLE和DEFERRED时，在事务提交时才验证，如果验证没通过，则报错，事务回滚。
3. novalidate, validate(default value)
定义是否对表中已经存在的数据作检查。
删除约束并插入一条脏数据：
SQL> alter table empx drop constraint fk_deptx;
Table altered.
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8000,'TOM','SALESMAN',7839,sysdate,2000,50);
1 row created.
SQL> commit;
Commit complete.
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno);
alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) deferrable initially deferred
*
ERROR at line 1:
ORA-02298: cannot validate (SCOTT.FK_DEPTX) - parent keys not found
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) deferrable initially deferred;
alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) deferrable initially deferred
*
ERROR at line 1:
ORA-02298: cannot validate (SCOTT.FK_DEPTX) - parent keys not found
语句中不带validate属性参数，默认创建的是validate的约束。由于有脏数据的存在，不管是创建延时还是非延时的约束都不成功。
SQL> alter table empx add constraint fk_deptx foreign key (deptno) references deptx(deptno) novalidate;
Table altered.
创建novalidate的约束成功。
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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18CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- ---------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED NOT DEFERRABLE IMMEDIATE NOT VALIDATED
SQL> select * from empx;
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87EMPNO 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 8000 TOM SALESMAN 7839 15-JUL-12 2000 50
有一条脏数据存在，看看能不能再增加一条：
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8001,'TOM','SALESMAN',7839,sysdate,2000,50);
insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8001,'TOM','SALESMAN',7839,sysdate,2000,50)
*
ERROR at line 1:
ORA-02291: integrity constraint (SCOTT.FK_DEPTX) violated - parent key not found
不能增加违反约束的数据，novalidate的约束只是对原来的数据库不做验证，但对新插入的数据还是要进行验证的。
4. disable, enalbe(default value)
启用和禁用constraint.如果在新建pk和uk时定义了disable,将不建立相应的索引.
SQL> alter table empx disable constraint fk_deptx;
Table altered.
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- ---------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX DISABLED NOT DEFERRABLE IMMEDIATE NOT VALIDATED
SQL> insert into empx (empno,ename,job,mgr,hiredate,sal,deptno) values (8001,'TOM','SALESMAN',7839,sysdate,2000,50);
1 row created.
SQL> commit;
Commit complete.
禁用了约束后，脏数据也能插入成功。
SQL> alter table empx enable constraint fk_deptx;
alter table empx enable constraint fk_deptx
*
ERROR at line 1:
ORA-02298: cannot validate (SCOTT.FK_DEPTX) - parent keys not found
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- ---------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX DISABLED NOT DEFERRABLE IMMEDIATE NOT VALIDATED
SQL> alter table empx enable novalidate constraint fk_deptx;
Table altered.
SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from user_constraints where table_name='EMPX';
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17CONSTRAINT_NAME COND STATUS DEFERRABLE DEFERRED VALIDATED ---------------- ---------------- ------------------------ ---------------- ---------------- ---------------- PK_EMPX ENABLED NOT DEFERRABLE IMMEDIATE VALIDATED FK_DEPTX ENABLED NOT DEFERRABLE IMMEDIATE NOT VALIDATED
如果有脏数据，启用约束时要同时设置novalidate。
由上面的实验得知，默认情况下，Oracle constraint是不开启延迟约束和原有数据保留验证的。
下列情况下可以使用这些特性：
1）批量数据导入、物化视图刷新的时候，事务量很大，而且存在数据规律前后颠倒的情况
此时，如果开启着立即约束应用的开关，可能存在一些暂时性的约束不满足的情况，从而影响到整个系统的运行。开启约束延迟验证，就可以帮助我们解决这个问题；
2）在历史数据移植
历史数据存在不规则的情况，很多时候难以满足我们新系统的数据完整性要求。可以使用not validate的方式，对历史数据不进行约束控制，而只针对新数据开启验证。
最后
以上就是坚定热狗最近收集整理的关于ORACLE约束的属性的全部内容，更多相关ORACLE约束内容请搜索靠谱客的其他文章。
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