MongoDB - List all collection from selected DB

There are two ways to do so, so far :

1 ) using  reference variable 'db'
     db.getCollectionNames()

2) using show command
    show collections

MongoDB : use database / switch to different database

MongoDB uses same syntax as SQL/MySQL to switch to different database :

MongoDB Syntax :
    use DATABASE_NAME
SQL Syntax :
     use DATABASE_NAME ;