How to avoid deletion of more than 1 row per request with trigger?

Question

I want to write a trigger which denies deletion of more than 1 row per request

Is it possible to write such trigger? If yes, can you help with an idea or code?

I am using oracle database 11g and writing in sqldeveloper

Orders Table

id
detail
orderdate

Answer 1

I'm not sure why you would want to do this (multi-row deletes are more efficient than single-row deletes), but you could use a compound trigger for this purpose, eg:

create table mytable (id number);

create or replace trigger one_row_per_delete
  for delete on mytable
  compound trigger

  row_count integer;

  before statement is
  begin
    row_count := 0;
  end before statement;

  before each row is
  begin
    row_count := row_count + 1;
  end before each row;

  after statement is
  begin
    if row_count > 1 then
      raise_application_error(-20000, 'Cannot delete more than one row per statement');
    end if;
  end after statement;

end one_row_per_delete;

Tested:

insert into mytable values (1);

1 row inserted.

insert into mytable values (2);

1 row inserted.

insert into mytable values (3);

1 row inserted.

delete mytable where id = 1;

1 row deleted.

delete mytable;

ORA-20000: Cannot delete more than one row per statement
ORA-06512: at "SCOTT.ONE_ROW_PER_DELETE", line 18
ORA-04088: error during execution of trigger 'SCOTT.ONE_ROW_PER_DELETE'

Answer 2

You can perform it with a trigger, for example

CREATE OR REPLACE TRIGGER denies_delete_trg
BEFORE DELETE
   ON table_name
DECLARE
   v_count_elements NUMBER := 0;

BEGIN
   SELECT COUNT(1) INTO v_count_elements
   FROM table_name
   WHERE contitions_of_delete;

   IF v_count_elements > 0 THEN
       RAISE_APPLICATION_ERROR (-20000,'Too rows to delete.'); 
   END IF;
END;