Wednesday, November 30, 2016

Delete Cascade with Recursive PL/SQL

If you need to delete all rows in a table that has parent keys for other tables' foreign keys, and the foreign keys constraints have not been defined with "on delete cascade", you can do a recursive delete with the following simple procedure.

This is typically something you will do only in a test or development database, and not in production. As always, it is a good thing to understand this procedure before you execute it:


create or replace procedure delete_cascade(
  p_table_name in user_tables.table_name%type) is
  l_pk user_constraints.constraint_name%type;
begin
  select constraint_name into l_pk
  from user_constraints
  where Constraint_Type='P'
  and table_name=upper(p_table_name);
  for c in (
  select table_name
  from user_constraints
  where R_CONSTRAINT_NAME=l_pk) loop
    delete_cascade(c.table_name);
  end loop;
  execute immediate 'delete from ' || upper(p_table_name);
exception when no_data_found then -- Tables without constraint
  execute immediate 'delete from ' || upper(p_table_name);;
end;
/




1 comment :

Oyvind Isene said...

As @DBoriented pointed out on Twitter, a foreign key may reference a unique key, so the code should look for constraints of type U as well.