You must insure that an instance of the SQL Server database is available for any type of SolidWorks Electrical installation. You can use an existing SQL Server database if it is already installed on the system, or install a new instance as part of the SolidWorks Electrical installation.
When you install a new instance of SQL Server, SolidWorks installation provides a free version of Microsoft SQL Server Express. This version is limited to 1 CPU, 1 GB of memory, and 10 GB of data. The memory and CPU limitations are sufficient to support 5 concurrent users.
If you install SQL Server Express Edition, ensure that the server software and hardware meet the requirements listed http://solidworks.com/System_Requirements.
However, if there are more 6 or more concurrent users on the same server, you should purchase and install a full version of SQL Server, and use the workflow described for installing SolidWorks Electrical with an existing instance of SQL Server.
For information about the SQL Server Express Edition, consult the Microsoft SQL Server documentation.