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https://bbs.fanruan.com/wenda/question/81901.html
参考
DAY(today())/(DATE(YEAR(TODAY()),MONTH(TODAY())+1,1)-DATE(YEAR(TODAY()),MONTH(TODAY()),1))
分数形式:
DAY(today()) +"/" +(DATE(YEAR(TODAY()),MONTH(TODAY())+1,1)-DATE(YEAR(TODAY()),MONTH(TODAY()),1))