Reference System.Data.SqlClient not found

Microsoft has removed System.Data.SqlClient from the default installation of Visual Studio (.NET Core). In order to use it, you must install from NuGet as install-package System.Data.SqlClient.  Once installed, this reference is available for use and code will compile.

Sources:

https://social.msdn.microsoft.com/Forums/en-US/ec2361a3-1931-4423-bf68-08b206ce67aa/reference-systemdatasqlclient-not-found?forum=netfxbcl