Reaching the tree END in oracle - sql

Question

I have one requirement...Suppose we have three table
1.A
primary key a_id
2.B
primary key b_id
foreign key a_id
3.C
primary key c_id
foreign key b_id
these tables contain 10 records each.
Need : Now i want to delete a specific record from each table.The record will be delete on a value supplied as a_id(primary key of table A).It will delete from A alright but how i can delete it from c as it does not contain a_id and this is only value known to us.
So how to do it...can anyone please let me know nay approach or anything.I need to delete a specific record from each table.starting point is a_id which is only thing known to us.
I am using oracle 10g and I cannot use any sys table. Thats a requirement as dba has given admin access.

Answer 1

you can do with the help of ON DELETE CASCADE option
see here here

Answer 2

CREATE TABLE A (a_id NUMBER, CONSTRAINT a_pk PRIMARY KEY (a_id));
CREATE TABLE B
(
b_id NUMBER
,a_id
,CONSTRAINT b_pk PRIMARY KEY (b_id)
,CONSTRAINT b_fk FOREIGN KEY (a_id) REFERENCES A (a_id)
);
CREATE TABLE C
(
C_id NUMBER
,b_id
,CONSTRAINT c_pk PRIMARY KEY (c_id)
,CONSTRAINT c_fk FOREIGN KEY (b_id) REFERENCES B (b_id)
);
--creating dummy data
insert into A select level from dual connect by level<11 ;
insert into B(b_id,a_id) select level+10,level from dual connect by level<11;
insert into C(c_id,b_id) select level+20,level+10 from dual connect by level<11;
CREATE OR REPLACE PROCEDURE delete_a(p_a_id IN a.id%TYPE)
IS
BEGIN
--delete record from C first
DELETE FROM C WHERE b_id IN (SELECT b_id from B where a_id =p_a_id);
--delete record from B
DELET FROM B WHERE a_id = p_a_id;
--delete from the main table
DELETE FROM C where a_id = p_a_id;
COMMIT;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('Error while delete the recods '||SQLERRM);
ROLLBACK;
END delete_a;
Note:I have not tested the code ,but will work with this approach

Answer 3

I use the table script as follows:
CREATE TABLE A (a_id NUMBER CONSTRAINT a_pk PRIMARY KEY,a_grade CHAR(1));
CREATE TABLE b
( b_id NUMBER ,
b_grade CHAR(1),
CONSTRAINT b_pk PRIMARY KEY(b_id),
CONSTRAINT b_fk FOREIGN KEY (b_id) REFERENCES A(a_id)
ON DELETE CASCADE );
CREATE TABLE c
( c_id NUMBER,
c_grade CHAR(1),
CONSTRAINT c_pk PRIMARY KEY(c_id),
CONSTRAINT c_fk FOREIGN KEY(c_id)
REFERENCES b(b_id)
ON DELETE CASCADE );
BEGIN
INSERT INTO A VALUES(1,'a');
INSERT INTO b VALUES(1,'b');
INSERT INTO c VALUES(1,'c');
end;
/*below is the query that you provide in the table a to delete */
DELETE FROM A WHERE a_id=1;-- all tables values are deleted (parent and childs)
SELECT * FROM A;
SELECT * FROM b;
SELECT * FROM c;
hope this is what you needed.