https://blog.csdn.net/AaronDev/article/details/103858939
db.getCollection("cal1.files") .aggregate({ $match:{ $and:[ {uploadDate:{$gte:ISODate("2019-12-30T00:00:00.303Z")}}, {uploadDate:{$lte:ISODate("2020-01-05T00:00:00.303Z")}}, ] } }, { $group: { _id : null, sum : { $sum: "$length" } } })