Attach or detach content databases in SharePoint 2010/2013 using Powershell

To attach an existing content database:

Mount-SPContentDatabase "contentdbname" -DatabaseServer "SQLserver" -WebApplication http://SiteName

Where:

• is the content database to be attached.
  
• is the name of the database server.
  
• http://SiteName is the name of the web application to which the content database is being attached.
  
  

To detach a content database:

Dismount-SPContentDatabase "contentdb name" 

Where is the name of the content database.