级联/删除

Question

我有一个表中有来自多个表的“附件列表”。当我删除主表中的主键时，它应该删除enrollid。这是真的，如果我有一个主表和一个从表。但是，如果我有多个主表并希望执行级联删除，则会抛出违反主键和外键的错误消息。因为在附件表中登记将不会在表1和表2中。

有没有什么办法可以在这个上实现级联或者我应该在删除表1和表2中的enrollid时使用附件中的常规删除方法。

表：附件 enrollid INT - 这是外键 ATTACHMENTNAME VARCHAR2（50）

主表1：department1 enrollid INT - 这是主键 DepartmentName的VARCHAR2（25）

主表2：department2 enrollid int - 这是主键 departmentadd varchar2（25）

在此先感谢您的帮助。

创建与某些数据插入的语句。

CREATE TABLE DEPARTMENT 
    ( 
    ENROLLID NUMBER, 
    DEPARTNAME VARCHAR2(100), 
    CONSTRAINT DEPARTMENT_PK PRIMARY KEY (ENROLLID) 
    ) ; 

    INSERT INTO DEPARTMENT (ENROLLID, DEPARTNAME) VALUES (1, 'DEPART1'); 
    INSERT INTO DEPARTMENT (ENROLLID, DEPARTNAME) VALUES (2, 'DEPART2'); 

CREATE TABLE DIVISION 
    ( 
    ENROLLID NUMBER, 
    DIVISIONNAME VARCHAR2(100), 
    CONSTRAINT DIVISION_PK PRIMARY KEY (ENROLLID) 
    );  

    INSERT INTO DIVISION (ENROLLID, DIVISIONNAME) VALUES (3, 'DIV1'); 
    INSERT INTO DIVISION (ENROLLID, DIVISIONNAME) VALUES (4, 'DIV2'); 


    CREATE TABLE ATTACHMENTS 
    ( 
    ENROLLID NUMBER, 
    FILENAME VARCHAR2(500), 
    CONSTRAINT ATTACHMENTS_FK FOREIGN KEY (ENROLLID) 
     REFERENCES Department(ENROLLID) ON DELETE CASCADE 
     --REFERENCES DIVISION(ENROLLID) ON DELETE CASCADE 
    ) 

    the above sql creates the table with foreign key constraint. but, it throws error message if include the second CASCADE statement. So, i commented the second reference. Then, i ran the below INSERT statements. The first two were inserted fine. third line threw an error message (ORA-02291 Integrity constraint violated - parent key not found). 

    INSERT INTO ATTACHMENTS (ENROLLID,FILENAME) VALUES (1, 'attachment1'); 
    INSERT INTO ATTACHMENTS (ENROLLID,FILENAME) VALUES (2, 'attachment1'); 
    INSERT INTO ATTACHMENTS (ENROLLID,FILENAME) VALUES (3, 'attachment1'); 
    INSERT INTO ATTACHMENTS (ENROLLID,FILENAME) VALUES (4, 'attachment1') 

;

Answer 1

为了实现您的目标，我认为您需要在附件表格和部门和分区表格之间添加一个附加表格。

事情是这样的，也许：

create table department 
    (dept_id number, 
    departname varchar2(100), 
    constraint department_pk primary key (dept_id) 
    ) ; 

    insert into department (dept_id, departname) values (1, 'DEPART1'); 
    insert into department (dept_id, departname) values (2, 'DEPART2'); 

create table division 
    (div_id number, 
    divisionname varchar2(100), 
    constraint division_pk primary key (div_id) 
    );  

    insert into division (div_id, divisionname) values (1, 'DIV1'); 
    insert into division (div_id, divisionname) values (2, 'DIV2'); 

create table enrollment 
    (enrollid number, 
    dept_id number, 
    div_id number, 
    constraint enrollment_pk primary key (enrollid), 
    constraint enrollment_dept_fk foreign key (dept_id) references department (dept_id), 
    constraint enrollment_div_fk foreign key (div_id) references division (div_id), 
    constraint enrollment_chk check (div_id is not null or dept_id is not null)); 

--- here, I have assumed that at least one of div_id and dept_id is populated. 
--- If it should be that only one of them can be populated, not both, then you'll need to change the check constraint accordingly. 


insert into enrollment (enrollid, dept_id, div_id) values (1, 1, null); 
insert into enrollment (enrollid, dept_id, div_id) values (2, 2, null); 
insert into enrollment (enrollid, dept_id, div_id) values (3, null, 1); 
insert into enrollment (enrollid, dept_id, div_id) values (4, null, 2); 

create table attachments 
    ( 
    enrollid number, 
    filename varchar2(500), 
    constraint attachments_fk foreign key (enrollid) 
    references enrollment (enrollid) on delete cascade 
    ); 

    insert into attachments (enrollid,filename) values (1, 'attachment1'); 
    insert into attachments (enrollid,filename) values (2, 'attachment2'); 
    insert into attachments (enrollid,filename) values (3, 'attachment3'); 
    insert into attachments (enrollid,filename) values (4, 'attachment4'); 

    commit; 

然后，当你从报名表中删除，你可以看到该行被自动从附件表中删除。

delete from enrollment where enrollid = 4; 

commit; 

select * from enrollment order by enrollid; 

    ENROLLID DEPT_ID  DIV_ID 
---------- ---------- ---------- 
     1   1   
     2   2   
     3      1 

select * from attachments order by enrollid; 

    ENROLLID FILENAME 
---------- ----------- 
     1 attachment1 
     2 attachment2 
     3 attachment3