为什么我得到PL / SQL触发器错误PLS-00103？

Question

如果已经有一些值，我写了一个不更新表字段的触发器：

CREATE TRIGGER DO_NOT_UPDATE BEFORE UPDATE ON CONCERNED_TABLE
FOR EACH ROW
BEGIN
   IF :OLD.CONCERNED_FIELD IS NOT NULL 
   THEN
      RAISE_APPLICATION_ERROR(-20182,'Concerned dataitem already exists!');
   END IF;
END;

编译时我遇到了这个错误：

LINE/COL ERROR
-------- -----------------------------------------------------------------
5/3      PLS-00103: Encountered the symbol "end-of-file" when expecting
         one of the following:
         ; <an identifier> <a double-quoted delimited-identifier>
         The symbol ";" was substituted for "end-of-file" to continue.

看起来是什么问题？我完全忽略了一些东西。