mongodb

1. use "Database" will create new database
2. 
db.createUser( { user: "root",
                 pwd: "root",
                 roles: [ { role: "clusterAdmin", db: "admin" },
                          { role: "readAnyDatabase", db: "admin" },
                          "readWrite"] }
               )
 will create a new user in this database.
 3. show dbs will list all the database
 
 4. db.movie_collection.aggregate( [ {$group:{_id:{year:"$year"},count:{$sum:1}}}] )
 5. db.customerCollection.aggregate( [ {$match:{city: "East Khalil"}},{$group:{_id:{city:"$city"},count:{$sum:1}}}] )
 6. db.movie_director_collection.find({"movie_id":{$in:[1]}})