1、$avg
计算平均值
基础语法:{ $avg:
{ $avg: [
注：
（1）$avg计算的时候会忽略非数值数据（包括缺失值）
（2）在$group中使用时，若expression为数组，$avg会忽略这个expression进行计算
（3）在其他管道符中使用时，对于单个expression，若其为数组，$avg会遍历整个数组进行计算；对于多个expression，若其中含数组，$avg会忽略这个expression
2、$sum
数字求和，
基础语法:{ $sum:
{ $sum: [
注：
（1）如果expression包含数值和非数值情况，$sum返回值为全部数值字段的和
（2）如果expression为不存在字段，$sum返回值为0
（3）如果expression全部为非数值情况，$sum返回值为全0
（4）在$group中使用时，若expression为数组，$sum会忽略这个expression进行计算
（5）在其他管道符中使用时，对于单个expression，若其为数组，$sum会遍历整个数组进行计算；对于多个expression，若其中含数组，$sum会忽略这个expression
3、$min
求最小值，
基础语法:{ $min:
{ $min: [
注：
（1）$min计算的时null值和空值不参与比较
（2）在$group中使用时，若expression为数组，$min会将expression当成一个整体进行比较
（3）在其他管道符中使用时，对于单个expression，若其为数组，$min会遍历整个数组进行比较；对于多个expression，若其中含数组，$min会忽略这个expression
4、$max
求最大值，
基础语法:{ $max:
{ $max: [
注：
（1）$max计算的时null值和空值不参与比较
（2）在$group中使用时，若expression为数组，$max会将expression当成一个整体进行比较
（3）在其他管道符中使用时，对于单个expression，若其为数组，$max会遍历整个数组进行比较；对于多个expression，若其中含数组，$max会忽略这个expression
上述内容可以在一下几个管道符中使用
$group$project-
$addFields(在3.4及以后的版本总可用) -
$set(在4.2及以后的版本总可用) -
$replaceRoot(在3.4及以后的版本总可用) -
$replaceWith(在4.2及以后的版本总可用) -
$matchstage that includes an$exprexpression
示例
在管道符$group中的应有
{"_id":1,"item":"a","price":10,"quantity":2, "arry":["1",2,3], "num":9, "num1":10 },
{"_id":2,"item":"b","price":20,"quantity":1, "arry":[4,5,6], "num":10, "num1":"11"},
{"_id":3,"item":"c","price":5, "quantity":5, "arry":[], "num":null,"num1":"12"},
{"_id":4,"item":"a","price":10,"quantity":10,"arry":[7,8,""], "num":11, "num1":["11","12","13"]},
{"_id":5,"item":"c","price":5, "quantity":10,"arry":["10","11"],"num":12, "num1":"14"},
{"_id":6,"item":"d","price":15,"quantity":10,"arry":[""], "num":"13","num1":"15"},
{"_id":7,"item":"d","price":15,"quantity":10,"arry":[12,""], "num":14 },
{"_id":8,"item":"d","price":15,"quantity":10,"arry":[""], "num":15, "num1":["11","9","8"] }
例一：求均值，求和
db.getCollection("test").aggregate([{
$group: {
_id: "$item",
//求均值
avg_Amount: { $avg: { $multiply: [ "$price", "$quantity" ] } },//两字段乘积
avg_quantity: { $avg: "$quantity" },//单字段
avg_arry: { $avg: "$arry" },//数组
avg_num: { $avg: "$num" },//涉及null值,字符串值，"item":"c"，"item":"d"
avg_num1: { $avg: "$num1" },//涉及数组、字符串、部分字段不存在，"item":"a"，"item":"d"
avg_num2: { $avg: "$num2" },//全部不存在值
//求和
sum_Amount: { $sum: { $multiply: [ "$price", "$quantity" ] } },//两字段乘积
sum_quantity: { $sum: "$quantity" },//单字段
sum_arry: { $sum: "$arry" },//数组
sum_num: { $sum: "$num" },//涉及null值,字符串值，"item":"c"，"item":"d"
sum_num1: { $sum: "$num1" },//涉及数组、字符串、部分字段不存在，"item":"a"，"item":"d"
sum_num2: { $sum: "$num2" },//全部不存在值
}
}])
运行结果
{"_id":"a","avg_Amount":60,"avg_quantity":6,"avg_arry":null,"avg_num":10,"avg_num1":10,"avg_num2":null,
"sum_Amount":120,"sum_quantity":12,"sum_arry":NumberInt("0"),"sum_num":20,"sum_num1":10,"sum_num2":NumberInt("0")},
{"_id":"b","avg_Amount":20,"avg_quantity":1,"avg_arry":null,"avg_num":10,"avg_num1":null,"avg_num2":null,
"sum_Amount":20,"sum_quantity":1,"sum_arry":NumberInt("0"),"sum_num":10,"sum_num1":NumberInt("0"),"sum_num2":NumberInt("0")},
{"_id":"c","avg_Amount":37.5,"avg_quantity":7.5,"avg_arry":null,"avg_num":12,"avg_num1":null,"avg_num2":null,
"sum_Amount":75,"sum_quantity":15,"sum_arry":NumberInt("0"),"sum_num":12,"sum_num1":NumberInt("0"),"sum_num2":NumberInt("0")},
{"_id":"d","avg_Amount":150,"avg_quantity":10,"avg_arry":null,"avg_num":14.5,"avg_num1":null,"avg_num2":null,
"sum_Amount":450,"sum_quantity":30,"sum_arry":NumberInt("0"),"sum_num":29,"sum_num1":NumberInt("0"),"sum_num2":NumberInt("0")}
运行结果
例二：最大值，最小值
db.getCollection("test").aggregate([{
$group: {
_id: "$item",
//最小值
min_Amount: { $min: { $multiply: [ "$price", "$quantity" ] } },//两字段乘积
min_quantity: { $min: "$quantity" },//单字段
min_arry: { $min: "$arry" },//数组
min_num: { $min: "$num" },//涉及null值,字符串值，"item":"c"，"item":"d"
min_num1: { $min: "$num1" },//涉及数组、字符串、部分字段不存在，"item":"a"，"item":"d"
min_num2: { $min: "$num2" },
//最大值
max_Amount: { $max: { $multiply: [ "$price", "$quantity" ] } },//两字段乘积
max_quantity: { $max: "$quantity" },//单字段
max_arry: { $max: "$arry" },//数组
max_num: { $max: "$num" },//涉及null值,字符串值，"item":"c"，"item":"d"
max_num1: { $max: "$num1" },//涉及数组、字符串、部分字段不存在，"item":"a"，"item":"d"
max_num2: { $max: "$num2" },//全部不存在值
}
}])
运行结果
//最小值
{"_id":"a","min_Amount":20, "min_quantity":2, "min_arry":[7,8,""],"min_num":9, "min_num1":10, "min_num2":null},
{"_id":"b","min_Amount":20, "min_quantity":1, "min_arry":[4,5,6], "min_num":10,"min_num1":"11","min_num2":null},
{"_id":"c","min_Amount":25, "min_quantity":5, "min_arry":[], "min_num":12,"min_num1":"12","min_num2":null},
{"_id":"d","min_Amount":150,"min_quantity":10,"min_arry":[12,""], "min_num":14,"min_num1":"15","min_num2":null
//最大值
{"_id":"a","max_Amount":100,"max_quantity":10,"max_arry":["1",2,3], "max_num":11, "max_num1":["11","12","13"],"max_num2":null},
{"_id":"b","max_Amount":20, "max_quantity":1, "max_arry":[4,5,6], "max_num":10, "max_num1":"11", "max_num2":null},
{"_id":"c","max_Amount":50, "max_quantity":10,"max_arry":["10","11"],"max_num":12, "max_num1":"14", "max_num2":null},
{"_id":"d","max_Amount":150,"max_quantity":10,"max_arry":[""], "max_num":"13","max_num1":["11","9","8"], "max_num2":null},
运行结果
在管道符$project中的应有
{"_id":1,"arry":["1",2,3], "num":9, "num1":10 },
{"_id":2,"arry":[4,5,6], "num":10, "num1":"11"},
{"_id":3,"arry":[""], "num":11, "num1":null},
{"_id":4,"arry":[7,8,""], "num":"12" },
{"_id":5,"arry":["10","11"],"num1":"14","num":null },
{"_id":6,"arry":[], "num1":"15" }
例三：求均值，求和
db.getCollection("test").aggregate([{
$project: {
//求均值
avg_num: { $avg: "$num" },//单字段
avg_arry: { $avg: "$arry" },//数组
avg_num_arry: { $avg: ["$num" ,"$arry"]},//数字和数组
avg_num_num1: { $avg: ["$num" ,"$num1"]},//涉及null值(_id:3、5),字符串值(_id:2、4、5、6)
avg_num_num2: { $avg: ["$num" ,"$num2"] },//涉及字段不存在
//求和
sum_num: { $sum: "$num" },//单字段
sum_arry: { $sum: "$arry" },//数组
sum_num_arry: { $sum: ["$num" ,"$arry"]},//数字和数组
sum_num_num1: { $sum: ["$num" ,"$num1"] },//涉及null值(_id:3、5),字符串值(_id:2、4、5、6)
sum_num_num2: { $sum: ["$num" ,"$num2"] },//涉及字段不存在
}
}])
运行结果
//求均值
{"_id":1,"avg_num":9, "avg_arry":2.5, "avg_num_arry":9, "avg_num_num1":9.5, "avg_num_num2":9},
{"_id":2,"avg_num":10, "avg_arry":5, "avg_num_arry":10, "avg_num_num1":10, "avg_num_num2":10},
{"_id":3,"avg_num":11, "avg_arry":null,"avg_num_arry":11, "avg_num_num1":11, "avg_num_num2":11},
{"_id":4,"avg_num":null,"avg_arry":7.5, "avg_num_arry":null,"avg_num_num1":null,"avg_num_num2":null},
{"_id":5,"avg_num":null,"avg_arry":null,"avg_num_arry":null,"avg_num_num1":null,"avg_num_num2":null},
{"_id":6,"avg_num":null,"avg_arry":null,"avg_num_arry":null,"avg_num_num1":null,"avg_num_num2":null},
//求和
{"_id":1,"sum_num":9,"sum_arry":5,"sum_num_arry":9,"sum_num_num1":19,"sum_num_num2":9},
{"_id":2,"sum_num":10,"sum_arry":15,"sum_num_arry":10,"sum_num_num1":10,"sum_num_num2":10},
{"_id":3,"sum_num":11,"sum_arry":NumberInt("0"),"sum_num_arry":11,"sum_num_num1":11,"sum_num_num2":11},
{"_id":4,"sum_num":NumberInt("0"),"sum_arry":15,"sum_num_arry":NumberInt("0"),"sum_num_num1":NumberInt("0"),"sum_num_num2":NumberInt("0")},
{"_id":5,"sum_num":NumberInt("0"),"sum_arry":NumberInt("0"),"sum_num_arry":NumberInt("0"),"sum_num_num1":NumberInt("0"),"sum_num_num2":NumberInt("0")},
{"_id":6,"sum_num":NumberInt("0"),"sum_arry":NumberInt("0"),"sum_num_arry":NumberInt("0"),"sum_num_num1":NumberInt("0"),"sum_num_num2":NumberInt("0")},
运行结果
例四：最大值，最小值
db.getCollection("test").aggregate([{
$project: {
//最小值
min_num: { $min: "$num" },//单字段
min_arry: { $min: "$arry" },//数组
min_num_arry: { $min: ["$num" ,"$arry"]},//数字和数组
min_num_num1: { $min: ["$num" ,"$num1"]},//涉及null值(_id:3、5),字符串值(_id:2、4、5、6)
min_num_num2: { $min: ["$num" ,"$num2"] },//涉及字段不存在
//最大值
max_num: { $max: "$num" },//单字段
max_arry: { $max: "$arry" },//数组
max_num_arry: { $max: ["$num" ,"$arry"]},//数字和数组
max_num_num1: { $max: ["$num" ,"$num1"]},//涉及null值(_id:3、5),字符串值(_id:2、4、5、6)
max_num_num2: { $max: ["$num" ,"$num2"] },//涉及字段不存在
}
}])
运行结果
//最小值
{"_id":1,"min_num":9, "min_arry":2, "min_num_arry":9, "min_num_num1":9, "min_num_num2":9},
{"_id":2,"min_num":10, "min_arry":4, "min_num_arry":10, "min_num_num1":10, "min_num_num2":10},
{"_id":3,"min_num":11, "min_arry":"", "min_num_arry":11, "min_num_num1":11, "min_num_num2":11},
{"_id":4,"min_num":"12","min_arry":7, "min_num_arry":"12", "min_num_num1":"12","min_num_num2":"12"},
{"_id":5,"min_num":null,"min_arry":"10","min_num_arry":["10","11"],"min_num_num1":"14","min_num_num2":null},
{"_id":6,"min_num":null,"min_arry":null,"min_num_arry":[], "min_num_num1":"15","min_num_num2":null},
//最大值
{"_id":1,"max_num":9, "max_arry":"1", "max_num_arry":["1",2,3], "max_num_num1":10, "max_num_num2":9},
{"_id":2,"max_num":10, "max_arry":6, "max_num_arry":[4,5,6], "max_num_num1":"11","max_num_num2":10},
{"_id":3,"max_num":11, "max_arry":"", "max_num_arry":[""], "max_num_num1":11, "max_num_num2":11},
{"_id":4,"max_num":"12","max_arry":"", "max_num_arry":[7,8,""], "max_num_num1":"12","max_num_num2":"12"},
{"_id":5,"max_num":null,"max_arry":"11","max_num_arry":["10","11"],"max_num_num1":"14","max_num_num2":null},
{"_id":6,"max_num":null,"max_arry":null,"max_num_arry":[], "max_num_num1":"15","max_num_num2":null}
运行结果