sql中的外键：Oracle

Question

Parent Table

id | name /// id primary key

1 | Quddus

Child Table

id | name /// id primary key as well as foreign key

1 | Quddus

Here , I have used on delete cascade . Thats why , if I delete any tuple from parent table , it's also deleted from child table . But if I try to update the id in parent table , it does not effect child table rather say ERROR!

So my question is by which way i can update parent table and child table at the same time .

Thanks! and Sorry cause I am not a good English writer !

Answer 1

There is no " on update cascade" in Oracle. You should write a trigger for update child table when you update parent table. look this site. you'll see example trigger for you. just write a trigger. https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:5773459616034

Answer 2

This looks like a bad design. If the child table's ID should follow the parent table's ID then why do you have a child table at all? You might just as well add the child table's columns to the parent table.

In a more common design the child table will have it's own ID (PK) column and another ID_Parent column to reference the parent table.

Also unusual is the need to update a PK column. Actually that's a definite NO.

Answer 3

Unfortunately there is nothing called cascade update in Oracle. So what you have to do is to create a trigger and then do the update:

CREATE TABLE t1(c1 number primary key);
CREATE TABLE t2(c2 number references t1(

INSERT INTO t1 VALUES(1);
INSERT INTO t2 VALUES(1);

CREATE TRIGGER Cascade_Update
    AFTER UPDATE OF c1 ON t1
    FOR EACH ROW
BEGIN
    UPDATE t2
    SET c2 = :new.c1
    WHERE c2 = :old.c1;
END;

Now do the update and it'll update the child table too.