MongoDB——分页排序聚合操作

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原始数据：

/* 1 */
{
    "_id" : ObjectId("5b604ac423cc834a5495d780"),
    "name" : "lhc",
    "age" : 78.0
}

/* 2 */
{
    "_id" : ObjectId("5b6068c94b008f4e969ef4fd"),
    "name" : "jay",
    "age" : 20.0
}

/* 3 */
{
    "_id" : ObjectId("5b6068cf4b008f4e969ef4fe"),
    "name" : "aaa",
    "age" : 10.0
}

/* 4 */
{
    "_id" : ObjectId("5b6068d64b008f4e969ef4ff"),
    "name" : "bbbb",
    "age" : 88.0
}

/* 5 */
{
    "_id" : ObjectId("5b6068de4b008f4e969ef500"),
    "name" : "weeee",
    "age" : 0.0
}

/* 6 */
{
    "_id" : ObjectId("5b6068e54b008f4e969ef501"),
    "name" : "weeee",
    "age" : 30.0
}

skip & limit

db.user.find().limit(1).skip(1); 

/* 1 */
{
    "_id" : ObjectId("5b6068c94b008f4e969ef4fd"),
    "name" : "jay",
    "age" : 20.0
}

sort

// 1 为升序排列，而 -1 是用于降序排列
db.user.find().sort({age:1}); 

/* 1 */
{
    "_id" : ObjectId("5b6068de4b008f4e969ef500"),
    "name" : "weeee",
    "age" : 0.0
}

/* 2 */
{
    "_id" : ObjectId("5b6068cf4b008f4e969ef4fe"),
    "name" : "aaa",
    "age" : 10.0
}

/* 3 */
{
    "_id" : ObjectId("5b6068c94b008f4e969ef4fd"),
    "name" : "jay",
    "age" : 20.0
}

/* 4 */
{
    "_id" : ObjectId("5b6068e54b008f4e969ef501"),
    "name" : "weeee",
    "age" : 30.0
}

/* 5 */
{
    "_id" : ObjectId("5b604ac423cc834a5495d780"),
    "name" : "lhc",
    "age" : 78.0
}

/* 6 */
{
    "_id" : ObjectId("5b6068d64b008f4e969ef4ff"),
    "name" : "bbbb",
    "age" : 88.0
}

聚合操作

aggregate用于聚合操作，语法格式：db.COLLECTION_NAME.aggregate(AGGREGATE_OPERATION),例如，求平均值：

db.user.aggregate([{$group:{_id:'$name',average:{$avg:'$age'}}}]);