完成以下PL/SQL块,功能是:使用游标,显示所有单价低于250元的玩具的单价。 DECLARE my_toy_price toys.toyprice%TYPE; CURSOR toy_cur IS SELECT toyprice FROM toys WHERE toyprice<250; BEGIN ______________ LOOP ________________________________________ EXIT WHEN toy_cur%NOTFOUND; DBMS_OUTPUT.PUT_LINE (toy_cur%ROWCOUNT || '. 玩具单价:' || my_toy_price); END LOOP; CLOSE toy_cur; END;