How to map part of table (only for specific columns) in Entity Framework?

No, you can’t.
The workaround is to create store procedure or view, the map from there

Exporting The Razor WebGrid To Excel

http://www.mikesdotnetting.com/Article/204/Exporting-The-Razor-WebGrid-To-Excel

@{
    Layout = null;
    var db = Database.Open("Northwind");
    var sql = "SELECT CustomerID, CompanyName, ContactName, Address, City, Country, Phone FROM Customers";
    var data = db.Query(sql);
    var grid = new WebGrid(data, canPage: false, canSort: false);
    Response.AddHeader("Content-disposition", "attachment; filename=report.xls");
    Response.ContentType = "application/octet-stream";
}
@grid.GetHtml(
    columns: grid.Columns(
        grid.Column("CustomerID", "ID"),
        grid.Column("CompanyName", "Company Name"),
        grid.Column("ContactName", "Contact Name"),
        grid.Column("Address"),
        grid.Column("City"),
        grid.Column("Country"),
        grid.Column("Phone")
    )
)