查找MongoDB中重复的Name值的最高分？
若要查找最大分数，请使用GROUP()将集合中的文档分组。让我们创建一个包含文档的集合-
> db.demo114.insertOne({"Score":60,"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2efc57d8f64a552dae6354")
}
> db.demo114.insertOne({"Score":87,"Nam+e":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2efc5ad8f64a552dae6355")
}
> db.demo114.insertOne({"Score":45,"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2efc5dd8f64a552dae6356")
}
> db.demo114.insertOne({"Score":67,"Name":"Chris"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2efc68d8f64a552dae6357")
}
> db.demo114.insertOne({"Score":38,"Name":"David"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e2efc74d8f64a552dae6358")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo114.find();
这将产生以下输出-
{ "_id" : ObjectId("5e2efc57d8f64a552dae6354"), "Score" : 60, "Name" : "Chris" }
{ "_id" : ObjectId("5e2efc5ad8f64a552dae6355"), "Score" : 87, "Name" : "Chris" }
{ "_id" : ObjectId("5e2efc5dd8f64a552dae6356"), "Score" : 45, "Name" : "David" }
{ "_id" : ObjectId("5e2efc68d8f64a552dae6357"), "Score" : 67, "Name" : "Chris" }
{ "_id" : ObjectId("5e2efc74d8f64a552dae6358"), "Score" : 38, "Name" : "David" }以下是查找最大值的查询。这将计算出重复名称值的最高得分，例如“Chris”和“David”-
> db.demo114.group(
... {key: {Name:true},
... reduce: function(c,p) {
... if (p.maximumScore < c.Score) {
... p.maximumScore = c.Score;
... }
... },
... initial: { maximumScore: 0 }}
... );这将产生以下输出-
[
{
"Name" : "Chris",
"maximumScore" : 87
},
{
"Name" : "David",
"maximumScore" : 45
}
]