How to combine Connection String via Parameters

We can include parameter reference in the data source connection string and allow the user to choose a data source for the report. 

For example, with an Expression-based connection string, a user who is running a Products report can select a data source for a particular county before running the report.

The following example illustrates the use of a data source expression in a SQL Server connection string. The example assumes you have created a report parameter named ServerName: 

="Data Source=" & Parameters! ServerName.Value & "; initial catalog=ProductsDB"