Re: Oracle Delete Trigger - Constrain Delete to 1 Row

not sure what version, so demo is on 9.2:

hr_at_O920.CSDB01.CS.NL> create or replace package apex_var as   2 reccnt pls_integer;
  3 procedure increase_reccnt;
  4 procedure called_trigger;
  5 end;
  6 /
Package created.

hr_at_O920.CSDB01.CS.NL> create or replace package body apex_var as   2 procedure increase_reccnt as
  3 begin
  4 apex_var.reccnt := apex_var.reccnt + 1;   5 end increase_reccnt;
  6 --
  7 procedure called_trigger as
  8 begin
  9 if apex_var.reccnt > 1 then
 10 raise_application_error (-20001,'Only 1 delete allowed');  11 end if;
 12 end called_trigger;
 13 --
 14 end apex_var;
 15 /
Package body created.

hr_at_O920.CSDB01.CS.NL> create or replace trigger bill   2 before delete on employees
  3 for each row
  4 begin
  5 apex_var.increase_reccnt;
  6 end;
  7 /
Trigger created.

hr_at_O920.CSDB01.CS.NL> create or replace trigger bill_as   2 before delete on employees
  3 begin
  4 apex_var.called_trigger;
  5 end;
  6 /
Trigger created.

hr_at_O920.CSDB01.CS.NL> set serveroutput on hr_at_O920.CSDB01.CS.NL> select count(*) from employees;

  COUNT(*)

       107

hr_at_O920.CSDB01.CS.NL> delete from employees where manager_id=124; delete from employees where manager_id=124 *
ERROR at line 1:

ORA-20001: Only 1 delete allowed
ORA-06512: at "HR.APEX_VAR", line 10
ORA-06512: at "HR.BILL_AS", line 2
ORA-04088: error during execution of trigger 'HR.BILL_AS'

hr_at_O920.CSDB01.CS.NL> select count(*) from employees;

  COUNT(*)

       107

I'll leave it up to you how you are going to catch the error

-- 
Regards,
Frank van Bortel