大数据基础之Mongodb（2）常用查询命令

1 下载

https://www.mongodb.com/download-center/community

比如：

https://fastdl.mongodb.org/linux/mongodb-linux-x86_64-4.0.9.tgz

2 连接

# cd $MONGODB_HOME
# bin/mongo master:27017/database_name

3 查询

1 count

>db.getCollection('table_name').find({}).count()

2 group by

>db.getCollection('table_name').aggregate([{"$group": {_id: "$column_name", count: {"$sum": 1}}}])

3 select by limit

>db.getCollection('table_name').find({}).limit(1).pretty()

4 select by condition ‘=’

>db.getCollection('table_name').find({"column_name": "column_value"})

5 select by condition ‘>’

>db.getCollection('table_name').find({"column_name":{$gt:"column_value"}}).pretty()

6 select by condition ‘or’

>db.getCollection('table_name').find({$or: [ {"column_name1":"column_value1"},{"column_name2":{$gt:"column_value2"}}]}).pretty()

7 select by date range

>db.getCollection('table_name').find({"create_time":{$gte:ISODate("2019-05-18T00:00:00Z"),$lt:ISODate("2019-05-19T00:00:00Z")}})

8 map reduce - 词频统计

统计信息

>db.table_name.mapReduce(function(){ emit(this.column,1);}, function(key, values){return Array.sum(values);}, {out:"post_total"})

输出结果

>db.table_name.mapReduce(function(){ emit(this.column,1);}, function(key, values){return Array.sum(values);}, {out:"post_total"}).find() 

默认只输出20行结果，然后需要不断输入it才能输出更多结果，如果想一次输出全部结果，可以先执行

>DBQuery.shellBatchSize = 100000;