SQL分组的问题

SELECT STR_TO_DATE(d1.redeemTime,'%Y-%m-%d') redeemTime,SUM(redeemMoney) redeemMoney,STATUS
FROM dingpackredeemlist
GROUP BY redeemTime,status

为什么用别名不行要写成
SELECT STR_TO_DATE(d1.redeemTime,'%Y-%m-%d') redeemTime,SUM(redeemMoney) redeemMoney,STATUS
FROM dingpackredeemlist
GROUP BY STR_TO_DATE(d1.redeemTime,'%Y-%m-%d'),status

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分组是根据你查询表(原始表)的字段来的，不是你查出表的字段