1) Web Application already exist and you want to change the Content DB.
2) Web application should be created with existing Content DB.
Let’s look at them one by one.
1: Web Application already exist and you want to change the Content DB:
It’s better to stop the application pool for this web application from IIS.
Delete the Content DB (if you don’t need it).
Open the SharePoint Management Shell (with elevated privileges) and run the following PS Command:
Mount-SPContentDatabase -Name WSS_Content_DB_ToAttach -WebApplication http://mywebapplication:port
The above command will attach the content Database and now execute the below PS command in same window.
This command will upgrade the DB to the final version of your SharePoint Farm.
To Learn how to use this command: Upgrade-SPContentDatabase -examples
2: Web application should be created with existing Content DB:
This is very simple. Just mention the name of existing content DB while creating the new Web Application in the Central Admin.
Optionally if desired you can execute the above command to upgrade it.
How to find Content DB Version:
If you dont have the version of the content db then you have to run the following script:
1: SELECT Version, UserName 2: FROM Versions 3: WHERE VersionId = ‘00000000-0000-0000-0000-000000000000’ 4: ORDER BY Id DESC
or open the version table directly (Not recommended).
WHERE VersionId = ‘00000000-0000-0000-0000-000000000000’
ORDER BY Id DESC
More About SharePoint Versions:
The below links could help you to find what is latest version released by Microsoft.
SharePoint 2010: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=224
SharePoint 2013: http://www.toddklindt.com/blog/Lists/Posts/Post.aspx?ID=346