查询文档（数据）

查询所有

> db.demo_collection.find()
{ "_id" : ObjectId("5fdbfdd854e1efc76f83e0a0"), "name" : "Eric" }
{ "_id" : ObjectId("5fdc016454e1efc76f83e0a1"), "demo" : "Demo" }
{ "_id" : ObjectId("5fdc458554e1efc76f83e0a2"), "name" : "coco", "type" : "drink", "count" : 100 }
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }
{ "_id" : ObjectId("5fdc477a54e1efc76f83e0a5"), "name" : "Lee" }
{ "_id" : ObjectId("5fdc477a54e1efc76f83e0a6"), "name" : "Chen" }

查询name为"一点点"的数据

> db.demo_collection.find({"name":"一点点"})
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

使用and条件查询，查询name为"一点点"并且type为"drink"的数据

db.demo_collection.find({"name":"一点点", "type": "drink"})
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

使用or条件查询

> db.demo_collection.find({$or:[{"name":"Lee"},{"name":"coco"}]})
{ "_id" : ObjectId("5fdc458554e1efc76f83e0a2"), "name" : "coco", "type" : "drink", "count" : 100 }
{ "_id" : ObjectId("5fdc477a54e1efc76f83e0a5"), "name" : "Lee" }

使用大于、大于等于，小于、小于等于，不等于查询

> db.demo_collection.find({"count":{$lt:50}})
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }
> db.demo_collection.find({"count":{$gte:50}})
{ "_id" : ObjectId("5fdc458554e1efc76f83e0a2"), "name" : "coco", "type" : "drink", "count" : 100 }
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

> db.demo_collection.find({"count":{$lt:100}})
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }
> db.demo_collection.find({"count":{$lte:100}})
{ "_id" : ObjectId("5fdc458554e1efc76f83e0a2"), "name" : "coco", "type" : "drink", "count" : 100 }
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

> db.demo_collection.find({"count":{$ne:100}})
{ "_id" : ObjectId("5fdbfdd854e1efc76f83e0a0"), "name" : "Eric" }
{ "_id" : ObjectId("5fdc016454e1efc76f83e0a1"), "demo" : "Demo" }
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }
{ "_id" : ObjectId("5fdc478154e1efc76f83e0a8"), "name" : "Zhang", "type" : "human" }

查询name中包含"点"

> db.demo_collection.find({"name": /点/}))
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

查询name中以"一"开头

> db.demo_collection.find({"name": /^一/})
{ "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"), "name" : "一点点", "type" : "drink", "count" : 50 }

使用pretty()链式方法，可使数据按格式化显示

> db.demo_collection.find({"name":"一点点"}).pretty()
{
        "_id" : ObjectId("5fdc46ab54e1efc76f83e0a4"),
        "name" : "一点点",
        "type" : "drink",
        "count" : 50
}

联合查询文档（数据）

插入数据

db.user.insertMany([
    {
        _id: ObjectId("5af2b2c6b138c267e414c072"),
        uid: "uid000",
        name: "小红",
        age: 26
    },
    {
        _id: ObjectId("5af2b2c6b138c267e414c073"),
        uid: "uid001",
        name: "小芳",
        age: 27
    }
]);

db.order.insertMany([
    {
        _id: ObjectId("4af2b2c6b138c267e414c071"),
        uid: "uid000",
        product: "产品1",
        money: 100
    },
    {
        _id: ObjectId("4af2b2c6b138c267e414c072"),
        uid: "uid000",
        product: "产品2",
        money: 200
    },
    {
        _id: ObjectId("4af2b2c6b138c267e414c073"),
        uid: "uid001",
        product: "产品1",
        money: 100
    },
    {
        _id: ObjectId("4af2b2c6b138c267e414c074"),
        uid: "uid001",
        product: "产品2",
        money: 200
    }
]);

联合查询

> db.user.aggregate([{$lookup: { from: "order", localField: "uid",  foreignField: "uid",  as: "orders"}}]).pretty()
{
        "_id" : ObjectId("5af2b2c6b138c267e414c072"),
        "uid" : "uid000",
        "name" : "小红",
        "age" : 26,
        "orders" : [
                {
                        "_id" : ObjectId("4af2b2c6b138c267e414c071"),
                        "uid" : "uid000",
                        "product" : "产品1",
                        "money" : 100
                },
                {
                        "_id" : ObjectId("4af2b2c6b138c267e414c072"),
                        "uid" : "uid000",
                        "product" : "产品2",
                        "money" : 200
                }
        ]
}
{
        "_id" : ObjectId("5af2b2c6b138c267e414c073"),
        "uid" : "uid001",
        "name" : "小芳",
        "age" : 27,
        "orders" : [
                {
                        "_id" : ObjectId("4af2b2c6b138c267e414c073"),
                        "uid" : "uid001",
                        "product" : "产品1",
                        "money" : 100
                },
                {
                        "_id" : ObjectId("4af2b2c6b138c267e414c074"),
                        "uid" : "uid001",
                        "product" : "产品2",
                        "money" : 200
                }
        ]
}

拆分orders

> db.user.aggregate([
...   { $lookup: { from: "order", localField: "uid", foreignField: "uid", as: "orders"}},
...   { $unwind: { path: "$orders", preserveNullAndEmptyArrays: true }}
... ]).pretty()
{
        "_id" : ObjectId("5af2b2c6b138c267e414c072"),
        "uid" : "uid000",
        "name" : "小红",
        "age" : 26,
        "orders" : {
                "_id" : ObjectId("4af2b2c6b138c267e414c071"),
                "uid" : "uid000",
                "product" : "产品1",
                "money" : 100
        }
}
{
        "_id" : ObjectId("5af2b2c6b138c267e414c072"),
        "uid" : "uid000",
        "name" : "小红",
        "age" : 26,
        "orders" : {
                "_id" : ObjectId("4af2b2c6b138c267e414c072"),
                "uid" : "uid000",
                "product" : "产品2",
                "money" : 200
        }
}
{
        "_id" : ObjectId("5af2b2c6b138c267e414c073"),
        "uid" : "uid001",
        "name" : "小芳",
        "age" : 27,
        "orders" : {
                "_id" : ObjectId("4af2b2c6b138c267e414c073"),
                "uid" : "uid001",
                "product" : "产品1",
                "money" : 100
        }
}
{
        "_id" : ObjectId("5af2b2c6b138c267e414c073"),
        "uid" : "uid001",
        "name" : "小芳",
        "age" : 27,
        "orders" : {
                "_id" : ObjectId("4af2b2c6b138c267e414c074"),
                "uid" : "uid001",
                "product" : "产品2",
                "money" : 200
        }
}

分组求和

> db.user.aggregate([
...   { $lookup: { from: "order", localField: "uid", foreignField: "uid", as: "orders" }},
...   { $unwind: { path: "$orders", preserveNullAndEmptyArrays: true }},
...   { $group: { _id: "$_id", name: { $first: "$name" }, age: { $first: "$age" }, money: { $sum: "$orders.money" }}}
... ]).pretty()
{
        "_id" : ObjectId("5af2b2c6b138c267e414c072"),
        "name" : "小红",
        "age" : 26,
        "money" : 300
}
{
        "_id" : ObjectId("5af2b2c6b138c267e414c073"),
        "name" : "小芳",
        "age" : 27,
        "money" : 300
}

联合查询后，独立显示数据项

>db.order.aggregate([
  { $lookup: { from: "user", localField: "uid", foreignField: "uid", as: "u" }}, 
  { $unwind: "$u" }, 
  { $addFields: { name: "$u.name" }}, 
  { $project: { _id: 1, product: 1, money: 1, name: 1 }}
]).pretty()