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法律研究如何在 MongoDB 中执行聚合排序？
为此，可以使用 aggregate() 方法和 $sort() 运算符。为了理解这个概念，我们使用文档创建一个集合。创建带有文档的集合的查询如下 −
> db.aggregationSortDemo.insertOne({"StudentId":98,"StudentFirstName":"John","StudentLastName":"Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90140c5705caea966c5587")
}
> db.aggregationSortDemo.insertOne({"StudentId":128,"StudentFirstName":"Carol","StudentLastName":"Taylor"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90141b5705caea966c5588")
}
> db.aggregationSortDemo.insertOne({"StudentId":110,"StudentFirstName":"David","StudentLastName":"Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90142f5705caea966c5589")
}
> db.aggregationSortDemo.insertOne({"StudentId":139,"StudentFirstName":"Chris","StudentLastName":"Brown"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90146a5705caea966c558a")
}
> db.aggregationSortDemo.insertOne({"StudentId":125,"StudentFirstName":"Sam","StudentLastName":"Williams"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9015695705caea966c558b")
}
> db.aggregationSortDemo.insertOne({"StudentId":139,"StudentFirstName":"Mike","StudentLastName":"Wilson"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90158e5705caea966c558c")
}在 find() 方法的帮助下，显示集合中的所有文档。查询如下 −
> db.aggregationSortDemo.find().pretty();
以下是输出 −
{
"_id" : ObjectId("5c90140c5705caea966c5587"),
"StudentId" : 98,
"StudentFirstName" : "John",
"StudentLastName" : "Smith"
}
{
"_id" : ObjectId("5c90141b5705caea966c5588"),
"StudentId" : 128,
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor"
}
{
"_id" : ObjectId("5c90142f5705caea966c5589"),
"StudentId" : 110,
"StudentFirstName" : "David",
"StudentLastName" : "Miller"
}
{
"_id" : ObjectId("5c90146a5705caea966c558a"),
"StudentId" : 139,
"StudentFirstName" : "Chris",
"StudentLastName" : "Brown"
}
{
"_id" : ObjectId("5c9015695705caea966c558b"),
"StudentId" : 125,
"StudentFirstName" : "Sam",
"StudentLastName" : "Williams"
}
{
"_id" : ObjectId("5c90158e5705caea966c558c"),
"StudentId" : 139,
"StudentFirstName" : "Mike",
"StudentLastName" : "Wilson"
}以下是 MongoDB 聚合排序的查询。
案例 1－当您需要按降序排列结果时。查询如下 −
> db.aggregationSortDemo.aggregate( {$group: {_id: '$StudentId',"TotalOccurrences": {$sum: 1}}}, {$sort: {_id: -1}} ).pretty();以下是输出
{ "_id" : 139, "TotalOccurrences" : 2 }
{ "_id" : 128, "TotalOccurrences" : 1 }
{ "_id" : 125, "TotalOccurrences" : 1 }
{ "_id" : 110, "TotalOccurrences" : 1 }
{ "_id" : 98, "TotalOccurrences" : 1 }案例 2 − 当您需要按升序排列结果时。查询如下 −
> db.aggregationSortDemo.aggregate( {$group: {_id: '$StudentId', "TotalOccurrences": {$sum: 1}}}, {$sort: {_id: 1}} ).pretty();以下是输出 −
{ "_id" : 98, "TotalOccurrences" : 1 }
{ "_id" : 110, "TotalOccurrences" : 1 }
{ "_id" : 125, "TotalOccurrences" : 1 }
{ "_id" : 128, "TotalOccurrences" : 1 }
{ "_id" : 139, "TotalOccurrences" : 2 }
更新于： 2019 年 7 月 30 日
207 次浏览
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