把下列语句中的"P"改成取最大值：{ "aggregate" : "collection", "pipeline" : [{ "$match" : { "meterNo" : { "$in" : [ "TC11223344_1_1"]}, "createTime" : { "$gte" : { "$date" : "2023-05-29T16:00:00Z"}, "$lt" : { "$date" : "2023-05-31T03:05:12Z"}}, "P" : { "$ne" : null}}}, { "$sort" : { "createTime" : 1}}, { "$project" : { "meterNo" : 1, "P" : { "$toDouble" : "$P"}, "createTime" : { "$dateToString" : { "date" : "$createTime", "format" : "%Y-%m-%d %H:00:00", "timezone" : "Asia/Shanghai"}}}}, { "$group" : { "_id" : { "meterNo" : "$meterNo", "createTime" : "$createTime"}, "meterNo" : { "$first" : "$meterNo"}, "createTime" : { "$first" : "$createTime"}, "P" : { "$avg" : "$P"}}}], "allowDiskUse" : true}

可以将语句中的"$avg"操作改成"$max"操作，即可将"P"改成取最大值。修改后的语句如下所示：

{ 
  "aggregate" : "collection", 
  "pipeline" : [
    { "$match" : { 
        "meterNo" : { "$in" : [ "TC11223344_1_1"]},
        "createTime" : { "$gte" : { "$date" : "2023-05-29T16:00:00Z"}, "$lt" : { "$date" : "2023-05-31T03:05:12Z"}},
        "P" : { "$ne" : null}
      }
    }, 
    { "$sort" : { "createTime" : 1}}, 
    { "$project" : { 
        "meterNo" : 1, 
        "P" : { "$toDouble" : "$P"}, 
        "createTime" : { "$dateToString" : { "date" : "$createTime", "format" : "%Y-%m-%d %H:00:00", "timezone" : "Asia/Shanghai"}}
      }
    }, 
    { "$group" : { 
        "_id" : { "meterNo" : "$meterNo", "createTime" : "$createTime"}, 
        "meterNo" : { "$first" : "$meterNo"}, 
        "createTime" : { "$first" : "$createTime"}, 
        "P" : { "$max" : "$P"}
      }
    }
  ], 
  "allowDiskUse" : true
}