飘零枫叶

摘要： 先插入测试数据：for(var i=1; i<20; i++){ var num=i%6; db.test.insert({_id:i,name:"user_"+i,age:num});}1.普通分组查询db.test.group({key:{age:true},initial:{num:0},$reduce:function(doc,prev){prev.num++}});db.runCommand({group:{ns:"test",key:{age:true},initial:{num:0},$reduce:function(doc,prev 阅读全文