Mongodb(二)

2019独角兽企业重金招聘Python工程师标准>>>

1.复杂的CURD

2.高级操作

  包括聚合和游标

•   聚合  常见的聚合操作有：count distinct group  mapReduce

 

> > db.person.count() 1 > db.person.count({"name":"java"}) 1 > db.person.count({"name":"c"}) 0

> db.person.distinct("age") [ 20, 24, 25 ] > db.person.distinct("name") [ "java", "c", "c++", "maven", "javascript", "node" ]

 

• 游标

 

• 索引

        通常，web系统有大量的CURD操作，而R是其中使用最频繁的操作，从算法上来说有5中经典的方法。

> db.person.remove() > db.peerson.fiind() Sun Mar 17 00:24:38 TypeError: db.peerson.fiind is not a function (shell):1 > db.peerson.find() > for(var i=0;i<100000;i++){ ... var rand=parseInt(i*Math.random()); ... db.person.insert({"name":"king"+i,"age":i}); ... } > db.person.find() { "_id" : ObjectId("51449d5d817c01aeaec52f8e"), "name" : "king0", "age" : 0 } { "_id" : ObjectId("51449d5d817c01aeaec52f8f"), "name" : "king1", "age" : 1 } { "_id" : ObjectId("51449d5d817c01aeaec52f90"), "name" : "king2", "age" : 2 } { "_id" : ObjectId("51449d5d817c01aeaec52f91"), "name" : "king3", "age" : 3 } { "_id" : ObjectId("51449d5d817c01aeaec52f92"), "name" : "king4", "age" : 4 } { "_id" : ObjectId("51449d5d817c01aeaec52f93"), "name" : "king5", "age" : 5 } { "_id" : ObjectId("51449d5d817c01aeaec52f94"), "name" : "king6", "age" : 6 } { "_id" : ObjectId("51449d5d817c01aeaec52f95"), "name" : "king7", "age" : 7 } { "_id" : ObjectId("51449d5d817c01aeaec52f96"), "name" : "king8", "age" : 8 } { "_id" : ObjectId("51449d5d817c01aeaec52f97"), "name" : "king9", "age" : 9 } { "_id" : ObjectId("51449d5d817c01aeaec52f98"), "name" : "king10", "age" : 10 } { "_id" : ObjectId("51449d5d817c01aeaec52f99"), "name" : "king11", "age" : 11 } { "_id" : ObjectId("51449d5d817c01aeaec52f9a"), "name" : "king12", "age" : 12 } { "_id" : ObjectId("51449d5d817c01aeaec52f9b"), "name" : "king13", "age" : 13 } { "_id" : ObjectId("51449d5d817c01aeaec52f9c"), "name" : "king14", "age" : 14 } { "_id" : ObjectId("51449d5d817c01aeaec52f9d"), "name" : "king15", "age" : 15 } { "_id" : ObjectId("51449d5d817c01aeaec52f9e"), "name" : "king16", "age" : 16 } { "_id" : ObjectId("51449d5d817c01aeaec52f9f"), "name" : "king17", "age" : 17 } { "_id" : ObjectId("51449d5d817c01aeaec52fa0"), "name" : "king18", "age" : 18 } { "_id" : ObjectId("51449d5e817c01aeaec52fa1"), "name" : "king19", "age" : 19 } Type "it" for more > it { "_id" : ObjectId("51449d5e817c01aeaec52fa2"), "name" : "king20", "age" : 20 }
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转载于:https://my.oschina.net/kingwjb/blog/114228