How to find child records is exists before to delete parent records.

Question

Dear Everyone,
I would like to ask you, is there any simple way to find child records is exists before to delete parent records.
I have a master table defined primary key and I have referenced that as foreign key in many tables.
I have used Delete_Record to delete but it isn't display the message 'child record exist' but it cleared the record from the form. So I need to know how to find child records is exists or not before to do delete_record so that I can display message in-case it exists.
I do know we can able to check in every table matching the column manually, but what if we use 100 of tables then it is not possible to check manually.
I am sure there must be simple way to find as how the oracle identifies when we execute delete query.
Please help me on this.
Thanks in advance.

Answer 1

Simple solution is to run the query I have given for all child tables or to try a single query for all child tables withj something like:
select <parent_key>
from <parent_table>
where <parent_key> in
          (select <foreign_key_1> from <child_table_1> union
           select <foreign_key_2> from <child_table_2> union
           ... );More complicate solution could be to change the foreign key constraints to cascade DELETE on parent table to child tables:
SQL>
SQL> create table p(x int primary key);
Table created.
SQL> create table c1(x1 int);
Table created.
SQL> create table c2(x2 int);
Table created.
SQL>
SQL> alter table c1 add constraint fk1 foreign key(x1) references p;
Table altered.
SQL> alter table c2 add constraint fk2 foreign key (x2) references p;
Table altered.
SQL>
SQL>
SQL> insert into p values(1);
1 row created.
SQL> insert into c1 values(1);
1 row created.
SQL> insert into c2 values(1);
1 row created.
SQL> commit;
Commit complete.
SQL>
SQL> alter table c1 drop constraint fk1;
Table altered.
SQL> alter table c2 drop constraint fk2;
Table altered.
SQL>
SQL> alter table c1 add constraint fk1 foreign key(x1) references p on delete cascade;
Table altered.
SQL> alter table c2 add constraint fk2 foreign key (x2) references p on delete cascade;
Table altered.
SQL>
SQL> delete p where x=1;
1 row deleted.
SQL> commit;
Commit complete.
SQL> select * from p;
no rows selected
SQL> select * from c1;
no rows selected
SQL> select * from c2;
no rows selected
SQL>Edited by: P. Forstmann on 27 oct. 2011 14:01