Shulou(Shulou.com)06/01 Report--

When grouping using aggregate, there are several grouping conditions, as follows

Native sql:

Db.test.aggregate (

{

$group: {

_ id: {name:'$name',pro:'$pro}

Total: {$sum:'$num'}

}

}

{

$project: {

Total:1

}

}

)

In java, it corresponds to the following:

/ / grouping by subjname and province DBObject groupFields = new BasicDBObject ("_ id", new BasicDBObject ("subjname", "$subjects.name"). Append ("province", "$province"); / / continue to add other operation groupFields.put such as sum,avg ("AvgScore", new BasicDBObject ("$avg", "$subjects.scores"))

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