mongo aggregate查询:
db.collection.aggregate({
$group:{
_id:"$id", //"$_id"代表引用集合中_id列
max_value:{$max:"$times"} //"$times"代表引用集合中times列
},
$match:{times:{$gte:100}}
})相当于sql查询:
select _id, max(times) from collection where times>=100