MongoDB aggregation Operations Group and Aggregate aggregation framework simple aggregation (10)

Group of aggregation operations

Grammar:

Db.collection.group (

{

Key:{key1:1,key2:1},

cond:{},

Reduce:function (Curr,result) {

},

initial:{},

Finalize:function () {

}

}

)

Key: Group Field

Cond: Query criteria

Reduce: aggregate function

Initial: Initialization

Finalize: Statistics a set of callback functions

#查询每个栏目下的商品数量

Db.goods.group (

{

Key:{cat_id:1},

cond:{},

Reduce:function (Curr,result) {

result.cnt + = 1;

},

initial:{cnt:0}

}

)

#查询每个栏目下价格高于50元的商品数量

Db.goods.group (

{

Key:{cat_id:1},

cond:{shop_price:{$GT: 50}},

Reduce:function (Curr,result) {

result.cnt + = 1;

},

initial:{cnt:0}

}

)

#每个栏目下的商品库存量 sum () operation

Db.goods.group (

{

Key:{cat_id:1},

cond:{},

Reduce:function (Curr,result) {

Result.num + = Curr.goods_number;

},

initial:{num:0}

}

)

#查询每个栏目最贵的商品价格, Max () operation

Db.goods.group (

{

Key:{cat_id:1},

cond:{},

Reduce:function (Curr, result) {

if (Curr.shop_price > Result.max) {

Result.max = Curr.shop_price;

}

},

initial:{max:0}

}

)

#查询每个栏目下商品的平均价格

Db.goods.group (

{

Key:{cat_id:1},

cond:{},

Reduce:function (Curr, result) {

result.cnt + = 1;

Result.sum + = Curr.shop_price;

},

initial:{sum:0,cnt:0},

Finalize:function (Result) {

Result.avg = result.sum/result.cnt;

}

}

)

Simple aggregation using the aggregate aggregation framework

#查询每个栏目下的商品数量

Db.collection.aggregate

(

[

{$group: {_id: "$cat _id", total:{$sum: 1}}

]

);

#查询goods下有多少条商品, select COUNT (*) from goods

Db.collection.aggregate

(

[

{$group: {_id:null,total:{$sum: 1}}}

]

)

#查询每个栏目下 the number of items with a price greater than 50 yuan

Db.collection.aggregate

(

[

{$match: {shop_price:{$gt: 50}}},

{$group: {_id: "$cat _id", total:{$sum: 1}}

]

)

#查询每个栏目下 the number of items with a price greater than 50 yuan

#并筛选出 "Number of items satisfying the condition" is greater than or equal to 3 columns

Db.collection.aggregate

(

[

{$match: {shop_price:{$gt: 50}}},

{$group: {_id: "$cat _id", total:{$sum: 1}},

{$match: {total:{$gte: 3}}}

]

)

#查询每个栏目下的库存量

Db.collection.aggregate

(

[

{$group: {_id: "$cat _id", total:{$sum: "$goods _number"}},

]

)

#查询每个栏目下的库存量, and sorted by inventory

Db.collection.aggregate

(

[

{$group: {_id: "$cat _id", total:{$sum: "$goods _number"}},

{$sort: {total:1}}

]

)

#查询每个栏目下的库存量, and sorted by inventory

Db.collection.aggregate

(

[

{$group: {_id: "$cat _id", total:{$sum: "$goods _number"}},

{$sort: {total:1}},

{$limit: 3}

]

)

#查询每个栏目的商品平均价格, and sorted by average price from high to low

Db.collection.aggregate

(

[

{$group: {_id: "$cat _id", avg:{$avg: "$shop _price"}},

{$sort: {avg:-1}}

]

)

MongoDB aggregation Operations Group and Aggregate aggregation framework simple aggregation (10)