mysql update和case语句结合

UPDATE test
SET avg_discount_area = (
CASE
WHEN avg_discount_area ='9.5折以上' THEN 0
WHEN avg_discount_area ='（8.0~8.5）折' THEN 1
WHEN avg_discount_area ='（6.5~8.0）折' THEN  2
WHEN avg_discount_area ='（4.0~6.5）折' THEN 3
WHEN avg_discount_area='（2.5~4.0）折' THEN 4
WHEN avg_discount_area='（1.0~2.5折）' THEN 5
WHEN avg_discount_area = '1折以下' THEN 6
WHEN avg_discount_area = '无数据' THEN 7
END
);