MongoDB简单使用-查询操作2

1查看当前数据库的文档

输入：

db.media.find()

系统返回：
{ "_id" : ObjectId("5aa490f053350e04ddbd6fa6"), "Type" : "Book", "Title" : "Definitive Guide to MongoDB 3rd ed.", "ISBN" : "978-1-4842-1183-0", "Publisher" : "Apress", "Author" : [ "Hows,David", "Plugge,Eelco", "Membrey,Peter", "Hawkins,Tim" ] }
{ "_id" : ObjectId("5aa4912953350e04ddbd6fa7"), "Type" : "CD", "Artist" : "Nirvana", "Title" : "Nevermind", "Tracklist" : [ { "Track" : "1", "Title" : "Smells Like Teen Spirit", "Length" : "5:02" }, { "Track" : "2", "Title" : "In Bloom", "Length" : "4:15" } ] }
{ "_id" : ObjectId("5aa4915453350e04ddbd6fa8"), "Type" : "Book", "Title" : "Definitive Guide to MongoDB 3rd ed.", "ISBN" : "978-1-4842-1183-1", "Publisher" : "Apress", "Author" : [ "Hows,David", "Plugge,Eelco", "Membrey,Peter", "Hawkins,Tim" ] }

2使用distinct()函数获取唯一值

db.media.distinct("Title")

系统返回：

[ "Definitive Guide to MongoDB 3rd ed.", "Nevermind" ]

3使用group()分组

db.media.group({key:{Title:true},initial:{Total:0},reduce:function(items,prev){prev.Total += 1}})

系统返回：

[
　　{
　　　　"Title" : "Definitive Guide to MongoDB 3rd ed.",
　　　　"Total" : 2
　　},
　　{
　　　　"Title" : "Nevermind",
　　　　"Total" : 1
　　}
]