SQL - Cascade on delete

Question

Hello Guys,
I have a small issue here. There is one parent table with several child tables associated to it. The problem is when defining the relationships the "cascade on delete" constraint was not defined. Now I want to enable it. I mean if I delete anything in the parent table, I want all the associated child rows should also get deleted.
Thanks in advance and appreciate your help.

Answer 1

I came up with the following, please note it has not been tested extensively. In addition it just generates the SQL, it doesn't execute it (which could be changed).
BEGIN
        FOR r IN
                SELECT  OWNER
                ,       CONSTRAINT_NAME
                ,       TABLE_NAME
                ,       PAR_OWNER
                ,       PAR_TABLE_NAME
                ,       MAX(SUBSTR(SYS_CONNECT_BY_PATH(COLUMN_NAME,', '),3)) KEEP (DENSE_RANK LAST ORDER BY RN) AS CHILD_COLS
                ,       MAX(SUBSTR(SYS_CONNECT_BY_PATH(PAR_COLUMN_NAME,', '),3)) KEEP (DENSE_RANK LAST ORDER BY RN) AS PAR_COLS
                FROM
                        SELECT  UC.OWNER
                        ,       UC.CONSTRAINT_NAME
                        ,       UC.TABLE_NAME
                        ,       UCC.COLUMN_NAME
                        ,       PC.OWNER                AS PAR_OWNER
                        ,       PC.TABLE_NAME           AS PAR_TABLE_NAME
                        ,       PCC.COLUMN_NAME         AS PAR_COLUMN_NAME
                        ,       ROW_NUMBER() OVER (PARTITION BY UC.OWNER, UC.CONSTRAINT_NAME, UC.TABLE_NAME ORDER BY UCC.POSITION) RN
                        FROM    USER_CONSTRAINTS        UC
                        JOIN    USER_CONS_COLUMNS       UCC     ON UCC.OWNER = UC.OWNER AND UCC.CONSTRAINT_NAME = UC.CONSTRAINT_NAME
                        JOIN    USER_CONSTRAINTS        PC      ON UC.R_OWNER = PC.OWNER AND UC.R_CONSTRAINT_NAME = PC.CONSTRAINT_NAME
                        JOIN    USER_CONS_COLUMNS       PCC     ON PCC.OWNER = PC.OWNER AND PCC.CONSTRAINT_NAME = PCC.CONSTRAINT_NAME AND PC.TABLE_NAME = PCC.TABLE_NAME AND PCC.POSITION = UCC.POSITION
                        WHERE   UC.DELETE_RULE != 'CASCADE'
                        AND     UC.CONSTRAINT_TYPE='R'
                START WITH RN = 1
                CONNECT BY PRIOR RN = RN -1 AND PRIOR CONSTRAINT_NAME = CONSTRAINT_NAME AND PRIOR TABLE_NAME = TABLE_NAME AND PRIOR OWNER = OWNER
                GROUP BY OWNER
                ,       CONSTRAINT_NAME
                ,       TABLE_NAME
                ,       PAR_OWNER
                ,       PAR_TABLE_NAME      
        LOOP
                -- Drop constraints
                DBMS_OUTPUT.PUT_LINE('ALTER TABLE ' || r.OWNER || '.' || r.TABLE_NAME || ' DROP CONSTRAINT ' || r.CONSTRAINT_NAME || ';');
                -- Re-create with ON DELETE CASCADE
                DBMS_OUTPUT.PUT_LINE('ALTER TABLE ' || r.OWNER || '.' || r.TABLE_NAME || ' ADD CONSTRAINT ' || r.constraint_name || ' FOREIGN KEY (' || r.CHILD_COLS || ') REFERENCES ' || r.PAR_OWNER || '.' || r.PAR_TABLE_NAME || '(' || r.PAR_COLS || ') ON DELETE CASCADE;');
        END LOOP;
END;With the following two tables:
CREATE TABLE PARENT(ID1 NUMBER, ID2 NUMBER, CONSTRAINT PARENT#PK PRIMARY KEY (ID2, ID1));
CREATE TABLE CHILD (ID1 NUMBER, ID2 NUMBER, CONSTRAINT CHILD#FK FOREIGN KEY (ID1, ID2) REFERENCES PARENT(ID1, ID2));It generated the following output:
ALTER TABLE TEST_USER.CHILD DROP CONSTRAINT CHILD#FK;
ALTER TABLE TEST_USER.CHILD ADD CONSTRAINT CHILD#FK FOREIGN KEY (ID2, ID1) REFERENCES TEST_USER.PARENT(ID2, ID1) ON DELETE CASCADE;