ORA-01722：无效数字PLSQL IMPLICIT CURSOR

Question

BEGIN 
  FOR v_region_rec IN (SELECT region_name, c.country_name
                         FROM regions r
                         JOIN countries c
                           ON r.region_id = c.country_id)
  LOOP
    DBMS_OUTPUT.PUT_LINE (v_region_rec.region_name || '  |  ' ||  v_region_rec.country_name );
  END LOOP;
END;

运行此plsql语句，但我真的不知道为什么它给了我ORA-01722：无效的数字