Question

I found it in a statement like this:

delete /*+ restrict_all_ref_cons  */ from table_1 where ...

Can anyone give some piece of information for what the hint is doing?

The database is an Oracle database 10.2.0.3.0.

Answer 1

The hint disables cascade deletion, so child rows will not be deleted from a child table when deleting from the parent.

See example here;

http://www.oracle-goldengate.info/archives/ogg-replication-for-delete-parent-table-with-fk-delete-cascade-option.html

create table s11 ( x int primary key );
create table s12 ( y int primary key, x references s11 on delete cascade );
insert into s11 values (1);
insert into s12 values (1, 1);
commit;
SQL> delete from s11;
1 row deleted.
SQL> select * from s12;
no rows selected <=========== when deleting parent row in s11, the child row in s12 is also deleted.

SQL> rollback;
Rollback complete.

SQL> delete /*+ RESTRICT_ALL_REF_CONS */ from s11;
1 row deleted.
SQL> select * from s12; <=========== with RESTRICT_ALL_REF_CONS hint, the child row will not be deleted.
Y X
---------- ----------
1 1