oracle使用cursor动态更新线上初始化数据

DECLARE
CURSOR c_res
IS SELECT B.PRESENT_NAME,B.PRESENT_PRESENT_LEFT_NUM,B.PRESENT_NUM FROM table B;
commitsum NUMBER(10);
leftNum NUMBER(4);
presentNum NUMBER(4);
BEGIN
commitsum :=0;
presentNum:=0;
FOR r_res IN c_res
LOOP
commitsum :=commitsum+1;
leftNum:=r_res.PRESENT_NUM-r_res.PRESENT_LEFT_NUM;
CASE
WHEN r_res.PRESENT_NAME='1';
THEN presentNum=100;
WHEN  r_res.PRESENT_NAME='2';
THEN presentNum=200;
END CASE;
UPDATE table set PRESENT_NUM=presentNum,PRESENT_LEFT_NUM = presentNum-leftNum
WHERE PRESENT_NAME = r_res.PRESENT_NAME;
IF(commitsum>100)
THEN
COMMIT;
commitsum:=0;
END IF;
END LOOP;
COMMIT;
END;