一個主表,帶了三個從表,一一關聯,A爲主表
A->B->C->D
從A表中刪除一條數據時，要把BCD表裏相關的數據都刪除的話
用什麼方法最好，必須用級聯刪除嗎？
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1.用觸發器；
2.建表時加關鍵字。比如B表某列關聯A表主鍵列，則：
create table b (col number references a(col) on delete cascade);
後面的C表D表類似處理。
分別在B C D創建外鍵時,都加上on delete cascade屬性
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級聯刪除我沒有用過,象你這種問題我覺得應該用一個存儲過程處理
而存儲過程中要用事務處理,要麼全部刪除成功,要麼什麼都不刪除
先刪除子表,然後再刪除主表
存儲過程要帶一個參數,參數爲主表的主鍵
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--做一個例子測試一下：
SQL> create table table3(id number(8) primary key,name varchar2(8));
Table created
SQL> insert into table3 values(1,'張三');
1 row inserted
SQL> insert into table3 values(2,'李四');
1 row inserted
SQL> commit;
Commit complete
SQL> create table table4(id2 number(6) primary key,id number(8),score number(8),
2 constraint FK_id foreign key (id) references table3(id));
Table created
SQL> insert into table4 values(10,1,3);
1 row inserted
SQL> insert into table4 values(11,2,2008);
1 row inserted
SQL> commit;
Commit complete
SQL> alter table table3 drop primary key cascade;
Table altered
SQL> select * from table3;
ID NAME
--------- --------
1 張三
2 李四
SQL> select * from table4;
ID2 ID SCORE
------- --------- ---------
10 1 3
11 2 2008
SQL> delete from table3 where id=1;
1 row deleted
SQL> commit;
Commit complete
SQL> select * from table3;
ID NAME
--------- --------
2 李四
SQL> select * from table4;
ID2 ID SCORE
------- --------- ---------
10 1 3
11 2 2008
SQL>
--從上述可以看出：刪除table3的主關鍵字id=1時，cascade並不能刪除table4表中的id=1的記錄。
--所以希望樓主還是使用觸發器的聯級觸發吧！不過調試時要思路清晰，多做測試。
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級聯刪除既能用外鍵on delete cascade, 也能用觸發器
但是觸發器消耗資源較多, 而且有經驗的DBA可能會知道,解發器會引起許多麻煩, 不建議使用
外鍵多級級聯刪除我測試是完全可以做到的:
SQL> create table t1
2 (
3 id varchar2(10),
4 name varchar2(10)
5 );
Table created
SQL> create table t2
2 (
3 id varchar2(10),
4 pid varchar2(10),
5 name varchar2(10)
6 );
Table created
SQL>
SQL> create table t3
2 (
3 id varchar2(10),
4 pid varchar2(10),
5 name varchar2(10)
6 );
Table created
SQL> alter table t1
2 add constraint pk_t1 primary key (id);
Table altered
SQL>
SQL> alter table t2
2 add constraint pk_t2 primary key (id);
Table altered
SQL>
SQL> alter table t3
2 add constraint pk_t3 primary key (id);
Table altered
SQL> alter table t2 add constraint FK_t1_t2 foreign key (pid) references t1(id) on delete cascade not deferrable;
Table altered
SQL> alter table t3 add constraint FK_t2_t3 foreign key (pid) references t2(id) on delete cascade not deferrable;
Table altered
SQL> insert into t1 values('1','aaa');
1 row inserted
SQL> insert into t1 values('2','bbb');
1 row inserted
SQL> insert into t2 values ('1','1','mmm');
1 row inserted
SQL> insert into t2 values ('2','1','nnn');
1 row inserted
SQL> insert into t3 values ('1','1','xxx');
1 row inserted
SQL> commit;
Commit complete
SQL> select * from t1;
ID NAME
---------- ----------
1 aaa
2 bbb
SQL> select * from t2;
ID PID NAME
---------- ---------- ----------
1 1 mmm
2 1 nnn
SQL> select * from t3;
ID PID NAME
---------- ---------- ----------
1 1 xxx
SQL> delete t1 where id = '1';
1 row deleted
SQL> commit;
Commit complete
SQL> select * from t1;
ID NAME
---------- ----------
2 bbb
SQL> select * from t2;
ID PID NAME
---------- ---------- ----------
SQL> select * from t3;
ID PID NAME
---------- ---------- ----------
SQL> rollback;
Rollback complete