一、准備知識
約束放置在表中，有以下五種約束:
NOT NULL 非空約束C 指定的列不允許為空值
UNIQUE 唯一約束U 指定的列中沒有重復值，或該表中每一個值或者每一組值都將是唯一的
PRIMARY KEY 主鍵約束P 唯一的標識出表的每一行,且不允許空值值,一個表只能有一個主鍵約束
FOREIGN KEY 外鍵約束R 一個表中的列引用了其它表中的列，使得存在依賴關系，可以指向引用自身的列
CHECK 條件約束C 指定該列是否滿足某個條件
約束命名規則
如果不指定約束名Oracle server 自動按照SYS_Cn 的格式指定約束名，也可手動指定，
推薦的約束命名是：約束類型_表名_列名。
NN：NOT NULL 非空約束，比如nn_emp_sal
UK：UNIQUE KEY 唯一約束
PK：PRIMARY KEY 主鍵約束
FK：FOREIGN KEY 外鍵約束
CK：CHECK 條件約束
外鍵約束是用來維護從表和主表的引用完整性的，所以外鍵約束要涉及兩個表。
FOREIGN KEY: 在表級指定子表中的列
REFERENCES: 標示在父表中的列
ON DELETE CASCADE: 當父表中的列被刪除時，子表中相對應的列也被刪除
ON DELETE SET NULL: 子表中相應的列置空
二、外鍵創建測試
foreign_main為主表
foreign_sub為從表
object_id做為foreign_sub的外鍵，參考主表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.
建議使用主表的主鍵做外鍵，即使不是主表的主鍵也應該是唯一約束的字段做為外鍵
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.
從表插入一條主表object_id中不存在的記錄測試
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
提示主表數據不存在，從表不能創建主表不存在的object_id以保證完整性
三、級聯刪除測試
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下仍然不能單獨更新主表外鍵字段
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模式下可以通過主表刪除外鍵字段數據關聯刪除從表數據
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
外鍵相關常用操作及參考文檔
建立外鍵
alter table 表名 add constraint 外鍵名 foreign key(從表外鍵字段) references foreign_main(主表外鍵字段);
drop表外鍵
alter table 表名 drop constraint 外鍵名;
通過外鍵找表
select * from user_constraints where constraint_type='R' and constraint_name=upper('外鍵名');
通過表找外鍵
select * from user_constraints where constraint_type='R' and table_name=upper('表名');
查找表的外鍵(包括名稱，引用表的表名和對應的鍵名，下面是分成多步查詢)：
select * from user_constraints c where c.constraint_type = 'R' and c.table_name = 要查詢的表
查詢引用表的鍵的列名：
select * from user_cons_columns cl where cl.constraint_name = 外鍵引用表的鍵名
外鍵約束臨時disabled
alter table 表名 disable constraint 外鍵名;
在SQL92標准中定義了幾種外鍵改變後，如何處理子表記錄的動作，其中包括：
限制Restrict：這種方式不允許對被參考的記錄的鍵值執行更新或刪除的操作;置為空Set to null：當參考的數據被更新或者刪除，那麼所有參考它的外鍵值被置為空;
置為默認值Set to default：當參考的數據被更新或者刪除，那麼所有參考它的外鍵值被置為一個默認值;
級聯Cascade：當參考的數據被更新，則參考它的值同樣被更新，當參考的數據被刪除，則參考它的子表記錄也被刪除;
不做操作No action：這種方式不允許更新或刪除被參考的數據。和限制方式的區別在於，這種方式的檢查發生在語句執行之後。Oracle默認才會的方式就是這種方式。
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 沒有禁用外鍵約束會出現以現錯誤
=============================================
2013-12-26 04:51:25 INFO OGG-00996 Oracle GoldenGate Delivery for Oracle, rep_app.prm: REPLICAT REP_APP started.
2013-12-26 04:51:25 WARNING OGG-00869 Oracle GoldenGate Delivery for Oracle, rep_app.prm: OCI Error ORA-02292: integrity constraint (SCOTT.FR_FOREIGN_SUB_OBJECT_ID) violated - child record found (status = 2292). DELETE FROM "SCOTT"."FOREIGN_MAIN" WHERE "OBJECT_ID" = :b0.
2013-12-26 04:51:25 WARNING OGG-01004 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Aborted grouped transaction on 'SCOTT.FOREIGN_MAIN', Database error 2292 (OCI Error ORA-02292: integrity constraint (SCOTT.FR_FOREIGN_SUB_OBJECT_ID) violated - child record found (status = 2292). DELETE FROM "SCOTT"."FOREIGN_MAIN" WHERE "OBJECT_ID" = :b0).
2013-12-26 04:51:25 WARNING OGG-01003 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Repositioning to rba 17426 in seqno 29.
2013-12-26 04:51:25 WARNING OGG-01154 Oracle GoldenGate Delivery for Oracle, rep_app.prm: SQL error 2292 mapping SCOTT.FOREIGN_MAIN to SCOTT.FOREIGN_MAIN OCI Error ORA-02292: integrity constraint (SCOTT.FR_FOREIGN_SUB_OBJECT_ID) violated - child record found (status = 2292). DELETE FROM "SCOTT"."FOREIGN_MAIN" WHERE "OBJECT_ID" = :b0.
2013-12-26 04:51:25 WARNING OGG-01003 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Repositioning to rba 17426 in seqno 29.
2013-12-26 04:51:25 ERROR OGG-01296 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Error mapping from SCOTT.FOREIGN_MAIN to SCOTT.FOREIGN_MAIN.
2013-12-26 04:51:25 WARNING OGG-01525 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Failed to open trace output file, 'gglog-REP_APP.dmp', error 13 (Permission denied).
2013-12-26 04:51:25 ERROR OGG-01668 Oracle GoldenGate Delivery for Oracle, rep_app.prm: PROCESS ABENDING.
2013-12-26 04:52:20 INFO OGG-00996 Oracle GoldenGate Delivery for Oracle, rep_app.prm: REPLICAT REP_APP started.
2013-12-26 04:52:20 WARNING OGG-00869 Oracle GoldenGate Delivery for Oracle, rep_app.prm: No unique key is defined for table 'FOREIGN_SUB'. All viable columns will be used to represent the key, but may not guarantee uniqueness. KEYCOLS may be used to define the key.
2013-12-26 04:52:20 WARNING OGG-01004 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Aborted grouped transaction on 'SCOTT.FOREIGN_SUB', Database error 1403 (OCI Error ORA-01403: no data found, SQL
2013-12-26 04:52:20 WARNING OGG-01003 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Repositioning to rba 17426 in seqno 29.
2013-12-26 04:52:20 WARNING OGG-01154 Oracle GoldenGate Delivery for Oracle, rep_app.prm: SQL error 1403 mapping SCOTT.FOREIGN_SUB to SCOTT.FOREIGN_SUB OCI Error ORA-01403: no data found, SQL
2013-12-26 04:52:20 WARNING OGG-01003 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Repositioning to rba 17426 in seqno 29.
2013-12-26 04:52:20 ERROR OGG-01296 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Error mapping from SCOTT.FOREIGN_SUB to SCOTT.FOREIGN_SUB.
2013-12-26 04:52:20 WARNING OGG-01525 Oracle GoldenGate Delivery for Oracle, rep_app.prm: Failed to open trace output file, 'gglog-REP_APP.dmp', error 13 (Permission denied).
2013-12-26 04:52:20 ERROR OGG-01668 Oracle GoldenGate Delivery for Oracle, rep_app.prm: PROCESS ABENDING.
