【mongoDB-数据库命令操作】---持续更新......

1. Create first database

The first time to use MongoDB database, you can use DATABASE_NAME to create a new Database if none exists, otherwise will switch to that database。

use DATABASE_NAME

Create first Dabase

> use first_dbswitched to db first_db

Check which database you are in, use “db” like this

> dbfirst_db

And you can show all database in your location

> show dbsadmin  0.000GBlocal  0.000GB

Wait! but why no your inserted db?

• it because you db(first_db) has nothing contents, so empty db will not shown while “show dbs”.

So, let’s insert one collection to our first_db.

> db.first.insert({name:"zhou changping"})WriteResult({ "nInserted" : 1 })> show dbsadmin     0.000GBfirst_db  0.000GBlocal     0.000GB

And check whether first collection is in first_db or not.

> show collectionsfirst

2. remove all collections in db
Now, we can use db.dropDatabase() cmd to remove you in db.
Now, we are in first_db, and it have first collection, then use db.dropDatabase().

> dbfirst_db> show collectionsfirst> db.dropDatabase(){ "dropped" : "first_db", "ok" : 1 }

Then, show collections will no longer any output this time.

如果要查询某个元素包含哪些value，可以用去重查询。

db.pr_summary.distinct("release")