drop down binding

Question

SqlCommand cmd = new SqlCommand("select FirstName+''+LastName from EmployeeMaster", con);

SqlDataAdapter dap = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

dap.Fill(ds);

ddldetails.DataSource = ds;

ddldetails.DataTextField = "FirstName+''+LastName";//Database table filed name for display in dropdown

ddldetails.DataBind();

 

 

getting an exception-

 

DataBinding: 'System.Data.DataRowView' does not contain a property with the name 'FirstName+''+LastName'. 

 

 

Please help me with this.