MongoDB University 第五周作业——aggregate聚合高级查询
db.grades.aggregate([{
$unwind : "$scores"
},
{
$match: {
$or: [
{"scores.type":"exam"},
{"scores.type":"homework"}
]
}
},
{
$group: {
_id:{
class_id: "$class_id",
student_id: "$student_id"
},
grade:{
$avg: "$scores.score"
}
}
},
{
$group: {
_id:{
class_id: "$_id.class_id"
},
avg_grade:{
$avg: "$grade"
}
}
},
{
$sort: { avg_grade : -1 }
},
{
$limit:1
}
]).pretty()
页:
[1]