存储过程常规语法：

实际业务例子：

CREATE OR REPLACE TRIGGER "TRI_B00_02_ONLY_GUID"
BEFORE/AFTER  INSERT OR UPDATE OR DELETE ON B00_02
FOR EACH ROW
 declare

  t_guid varchar2(300) := ''; --GUID
  t_cnt int := 0;

BEGIN

  t_guid := :NEW.B00_02_09;

  if t_guid is not null then
    select count(1) into t_cnt from b00_02 t where t.b00_02_09 = t_guid;
    if t_cnt > 0 then
      raise_application_error('-20001', 'GUID已经存在，不允许插入！');
    end if;
  end if;

END;