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关于oracle外键引用与goldengate

时间:2021-07-01 10:21:17 帮助过:36人阅读

一、准备知识 约束放置在表中,有以下五种约束: NOT NULL 非空约束C 指定的列不允许为空值 UNIQUE 唯一约束U 指定的列中没有重复值,或该表中每一个值或者每一组值都将是唯一的 PRIMARY KEY 主键约束P 唯一的标识出表的每一行,且不允许空值值,一个表只能有一

  一、准备知识

  约束放置在表中,有以下五种约束:

  NOT NULL 非空约束C 指定的列不允许为空值

  UNIQUE 唯一约束U 指定的列中没有重复值,或该表中每一个值或者每一组值都将是唯一的

  PRIMARY KEY 主键约束P 唯一的标识出表的每一行,且不允许空值值,一个表只能有一个主键约束

  FOREIGN KEY 外键约束R 一个表中的列引用了其它表中的列,使得存在依赖关系,可以指向引用自身的列

  CHECK 条件约束C 指定该列是否满足某个条件

  约束命名规则

  如果不指定约束名Oracle server 自动按照SYS_Cn 的格式指定约束名,也可手动指定,

  推荐的约束命名是:约束类型_表名_列名。

  NN:NOT NULL 非空约束,比如nn_emp_sal

  UK:UNIQUE KEY 唯一约束

  PK:PRIMARY KEY 主键约束

  FK:FOREIGN KEY 外键约束

  CK:CHECK 条件约束

  外键约束是用来维护从表和主表的引用完整性的,所以外键约束要涉及两个表。

  FOREIGN KEY: 在表级指定子表中的列

  REFERENCES: 标示在父表中的列

  ON DELETE CASCADE: 当父表中的列被删除时,子表中相对应的列也被删除

  ON DELETE SET NULL: 子表中相应的列置空

  二、外键创建测试

  foreign_main为主表

  foreign_sub为从表

  object_id做为foreign_sub的外键,参考主表foreign_main的object_id值

  SQL> create table foreign_main as select object_id from all_objects;

  Table created.

  SQL> select count(*) from foreign_main;

  COUNT(*)

  ----------

  49571

  SQL> create table foreign_sub as select object_id,object_name from all_objects;

  Table created.

  建议使用主表的主键做外键,,即使不是主表的主键也应该是唯一约束的字段做为外键

  SQL> alter table foreign_main add constraint pk_fsid primary key(object_id);

  Table altered.

  SQL> delete from foreign_sub where object_name = 'FOREIGN_MAIN';

  1 row deleted.

  SQL> commit;

  Commit complete.

  SQL> alter table foreign_sub add constraint fr_fssid foreign key(object_id) references foreign_main(object_id);

  Table altered.

  从表插入一条主表object_id中不存在的记录测试

  SQL> insert into foreign_sub values(1,'ts');

  insert into foreign_sub values(1,'ts')

  *

  ERROR at line 1:

  ORA-02291: integrity constraint (TEST.FR_FSSID) violated - parent key not found

  提示主表数据不存在,从表不能创建主表不存在的object_id以保证完整性

  三、级联删除测试

  SQL> alter table foreign_sub drop constraint fk_fs_oid;

  Table altered.

  SQL> alter table foreign_sub add constraint fk_fs_oid foreign key(object_id) references foreign_main(object_id) on delete cascade;

  Table altered.

  cascade下仍然不能单独更新主表外键字段

  SQL> update foreign_main set object_id=52012 where object_id=52010;

  update foreign_main set object_id=52012 where object_id=52010

  *

  ERROR at line 1:

  ORA-02292: integrity constraint (TEST.FK_FS_OID) violated - child record found

  cascade模式下可以通过主表删除外键字段数据关联删除从表数据

  SQL> select * from foreign_sub where object_id=52010;

  OBJECT_ID OBJECT_NAME

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

  52010 IDX_BJNAME

  SQL> delete from foreign_main where object_id=52010;

  1 row deleted.

  SQL> commit;

  Commit complete.

  SQL> select * from foreign_sub where object_id=52010;

  no rows selected

  外键相关常用操作及参考文档

  建立外键

  alter table 表名 add constraint 外键名 foreign key(从表外键字段) references foreign_main(主表外键字段);

  drop表外键

  alter table 表名 drop constraint 外键名;

  通过外键找表

  select * from user_constraints where constraint_type='R' and constraint_name=upper('外键名');

  通过表找外键

  select * from user_constraints where constraint_type='R' and table_name=upper('表名');

  查找表的外键(包括名称,引用表的表名和对应的键名,下面是分成多步查询):

  select * from user_constraints c where c.constraint_type = 'R' and c.table_name = 要查询的表

  查询引用表的键的列名:

  select * from user_cons_columns cl where cl.constraint_name = 外键引用表的键名

  外键约束临时disabled

  alter table 表名 disable constraint 外键名;

  在SQL92标准中定义了几种外键改变后,如何处理子表记录的动作,其中包括:

  限制Restrict:这种方式不允许对被参考的记录的键值执行更新或删除的操作;置为空Set to null:当参考的数据被更新或者删除,那么所有参考它的外键值被置为空;

  置为默认值Set to default:当参考的数据被更新或者删除,那么所有参考它的外键值被置为一个默认值;

  级联Cascade:当参考的数据被更新,则参考它的值同样被更新,当参考的数据被删除,则参考它的子表记录也被删除;

  不做操作No action:这种方式不允许更新或删除被参考的数据。和限制方式的区别在于,这种方式的检查发生在语句执行之后。Oracle默认才会的方式就是这种方式。

  Col OWNER FOR A6

  COL R_OWNER FOR A6

  COL TABLE_NAME FOR A15

  select OWNER, TABLE_NAME, CONSTRAINT_NAME, CONSTRAINT_TYPE, R_OWNER, R_CONSTRAINT_NAME, DELETE_RULE from user_constraints where table_name in ('FOREIGN_MAIN', 'FOREIGN_SUB');

  Select CONSTRAINT_NAME from user_constraints e where e.table_name='IMS_COLUMN' and owner='WSJD_ELMS6';

  Select b.table_name,b.column_name, A.CONSTRAINT_TYPE, C.TABLE_NAME from user_constraints a, user_cons_columns b, user_constraints C

  WHERE a.constraint_name = b.constraint_name AND

  A.R_CONSTRAINT_NAME = C.CONSTRAINT_NAME

  AND a.r_constraint_name IN (Select CONSTRAINT_NAME from user_constraints e where e.table_name='FOREIGN_MAIN' and owner='SCOTT');

  create table foreign_sub as select object_id, object_name from user_objects;

  create table foreign_main as select object_id from foreign_sub;

  alter table foreign_main add constraint pk_foreign_main_object_id primary key(object_id);

  alter table foreign_sub add constraint fr_foreign_sub_object_id foreign key(object_id) references foreign_main(object_id) on delete cascade;

  alter table foreign_sub drop constraint fr_foreign_sub_object_id;

  alter table foreign_sub disable constraint fr_foreign_sub_object_id;

  如在goldengate 没有禁用外键约束会出现以现错误

  =============================================

  2013-12-26 04:51:25 INFO OGG-00996 Oracle GoldenGate Delivery for Oracle, rep_app.prm: REPLICAT REP_APP started.

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