How to get the connection String from a database

A very simple way to retrieve a connection string, is to create a text file, change the extension from .txt to .udl.

Double-clicking the .udl file will open the Data Link Properties wizard.

Configure and test the connection to your database server.

Close the wizard and open the .udl file with the text editor of your choice and simply copy the connection string (without the Provider=<driver>part) to use it in your C# application.

sample udl file content

[oledb]
; Everything after this line is an OLE DB initstring
Provider=SQLNCLI11.1;Integrated Security=SSPI;Persist Security Info=False;User ID="";Initial Catalog=YOURDATABASENAME;Data Source=YOURSERVERNAME;Initial File Name="";Server SPN=""

what you need to copy from it

Integrated Security=SSPI;Initial Catalog=YOURDATABASENAME;Data Source=YOURSERVERNAME;

If you want to specify username and password you can adopt from other answers.

Tutorial: https://teusje.wordpress.com/2012/02/21/how-to-test-an-sql-server-connection/

Open SQL Server Management Studio and run following query. You will get connection string:

select
    'data source=' + @@servername +
    ';initial catalog=' + db_name() +
    case type_desc
        when 'WINDOWS_LOGIN' 
            then ';trusted_connection=true'
        else
            ';user id=' + suser_name() + ';password=<<YourPassword>>'
    end
    as ConnectionString
from sys.server_principals
where name = suser_name()

The easiest way to get the connection string is using the "Server Explorer" window in Visual Studio (menu View, Server Explorer) and connect to the server from that window.

Then you can see the connection string in the properties of the connected server (choose the connection and press F4 or Alt+Enter or choose Properties on the right click menu).

Advanced connection string settings: when creating the connection, you can modify any of the advanced connection string options, like MARS, resiliency, timeot, pooling configuration, etc. by clicking on the "Advanced..." button on the bottom of the "Add connection" dialog. You can access this dialog later by right clicking the Data Connection, and choosing "Modify connection...". The available advanced options vary by server type.

If you create the database using SQL Server Management Studio, the database will be created in a server instance, so that, to deploy your application you'll have to make a backup of the database and deploy it in the deployment SQL Server. Alternatively, you can use a data file using SQL Server Express (localDB in SQL Server 2012), that will be easily distributed with your app.

I.e. if it's an ASP.NET app, there's an App_Datafolder. If you right click it you can add a new element, which can be a SQL Server Database. This file will be on that folder, will work with SQL Express, and will be easy to deploy. You need SQL Express / localDB installed on your machine for this to work.