一、概述
MongoDB聚合框架（Aggregation Framework）是一个计算框架，它可以：
①：作用在一个或者几个集合上;
②：对集合中的数据进行一系列的运算;
③：将这些数据转化为期望的形式;
从效果而言，聚合框架相当于SQL中的 group by、left outer join、as等
二、聚合
2.1、管道（Pipeline）和步骤（Stage）
整个聚合运算过程称为管道（Pipeline），它是由多个步骤（Stage）组成的，每个管道：
①：接受一系列文档（原始数据）；
②：每个步骤对这些文档进行一系列运算；
③：结果文档输出给下一个步骤；
2.2、基本格式
pipline = [$stage1,$stage2,...$stageN]
db.<COLLECTION>.aggregate(
pipline,
{ options }
);2.3、常见步骤
2.3.1、常见步骤中的运算符
2.4、少见步骤
2.5、使用场景
聚合查询可以用于OLAP和OLTP场景，例如：
2.6、MQL常用步骤与SQL对比
2.6.1、vs1
2.6.2、vs2
2.6.3、特有步骤$unwind
2.6.4、特有步骤$bucket
2.6.5、特有步骤$facet
三、实验一
3.1、初始化数据
db.orders.insert(
[
{
"street": "西兴街道",
"city": "杭州",
"state": "浙江省",
"country": "中国",
"zip": "24344-1715",
"phone": "18866668888",
"name": "李白",
"userId": "3573",
"orderDate": "2019-01-02 03:20:08.805",
"status": "completed",
"shippingFee": 8.00,
"orderLines": [{
"product": "iPhone5",
"sku": "2001",
"qty": 1,
"price": 100.00,
"cost": 100.00
},
{
"product": "iPhone5s",
"sku": "2002",
"qty": 2,
"price": 200.00,
"cost": 400.00
},
{
"product": "iPhone6",
"sku": "2003",
"qty": 1,
"price": 300.00,
"cost": 300.00
},
{
"product": "iPhone6s",
"sku": "2004",
"qty": 2,
"price": 400.00,
"cost": 800.00
},
{
"product": "iPhone8",
"sku": "2005",
"qty": 2,
"price": 500.00,
"cost": 1000.00
}
],
"total": 2600
},
{
"street": "长河街道",
"city": "杭州",
"state": "浙江省",
"country": "中国",
"zip": "24344-1716",
"phone": "18866668881",
"name": "杜甫",
"userId": "3574",
"orderDate": "2019-02-02 13:20:08.805",
"status": "completed",
"shippingFee": 5.00,
"orderLines": [{
"product": "iPhone5",
"sku": "2001",
"qty": 1,
"price": 100.00,
"cost": 100.00
},
{
"product": "iPhone5s",
"sku": "2002",
"qty": 2,
"price": 200.00,
"cost": 400.00
},
{
"product": "iPhone6",
"sku": "2003",
"qty": 1,
"price": 300.00,
"cost": 300.00
},
{
"product": "iPhone6s",
"sku": "2004",
"qty": 2,
"price": 400.00,
"cost": 800.00
},
{
"product": "iPhone8",
"sku": "2005",
"qty": 2,
"price": 500.00,
"cost": 1000.00
}
],
"total": 2600
},
{
"street": "浦沿街道",
"city": "杭州",
"state": "浙江省",
"country": "中国",
"zip": "24344-1717",
"phone": "18866668882",
"name": "王安石",
"userId": "3575",
"orderDate": "2019-03-02 14:20:08.805",
"status": "completed",
"shippingFee": 20.00,
"orderLines": [{
"product": "iPhone5",
"sku": "2001",
"qty": 1,
"price": 100.00,
"cost": 100.00
},
{
"product": "iPhone5s",
"sku": "2002",
"qty": 2,
"price": 200.00,
"cost": 400.00
},
{
"product": "iPhone6",
"sku": "2003",
"qty": 1,
"price": 300.00,
"cost": 300.00
},
{
"product": "iPhone6s",
"sku": "2004",
"qty": 2,
"price": 400.00,
"cost": 800.00
},
{
"product": "iPhone12 ProMax",
"sku": "2006",
"qty": 1,
"price": 1500.00,
"cost": 1500.00
}
],
"total": 3100
},
{
"street": "长庆街道",
"city": "杭州",
"state": "浙江省",
"country": "中国",
"zip": "24344-1717",
"phone": "18866668883",
"name": "苏东坡",
"userId": "3576",
"orderDate": "2019-04-02 15:20:08.805",
"status": "completed",
"shippingFee": 10.00,
"orderLines": [
{
"product": "iPhone6s",
"sku": "2004",
"qty": 2,
"price": 400.00,
"cost": 800.00
},
{
"product": "iPhone12 ProMax",
"sku": "2006",
"qty": 1,
"price": 1500.00,
"cost": 1500.00
}
],
"total": 2300
}
]
)3.2、案例一：计算到目前为止的所有订单的总销售额
db.orders.aggregate(
[
{
$group:{
_id: null,
total: {$sum:"$total"}
}
}
]
) 
3.3、案例二：查询2019年第一季度(1月1日-3月31日)已完成订单(completed)的订单总金额和订单总数
db.orders.aggregate(
[
{
'$match': {
'status': 'completed',
'orderDate': {
'$gte': '2019-01-01',
'$lt': '2019-04-01'
}
}
}, {
'$group': {
'_id': null,
'total': {
'$sum': '$total'
},
'shippingFee': {
'$sum': '$shippingFee'
},
'count': {
'$sum': 1
}
}
}, {
'$project': {
'grandTotal': {
'$add': [
'$total', '$shippingFee'
]
},
'_id': 0
}
}
]
)
