how to hide empty columns in gridview

What you can do is check the columns for NULL or empty in RowDataBound() event of GridView and hide the columns accordingly. In the event method check first for DataRow like this and repeat for other columns

if (e.Row.RowType == DataControlRowType.DataRow)
            {
               // To hide the first column
               string vToCheck = e.Row.Cells[0].ToString();
               if(string.IsNullorEmpty(vToCheck) )
                {
                gridView.Columns[0].Visible = false;     
                }

            }

Please see:
https://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.datacontrolfield.visible%28v=vs.110%29.aspx[^],
https://msdn.microsoft.com/en-us/library/system.web.ui.control.visible(v=vs.110).aspx[^].

As you can see, you can change visibility of any instance of DataControlField or any Control, including TableCell. Then look at the structure of the table. It has Rows and Controls properties, and the cells are the elements of rows collection. Scan all data in columns in questions, show or hide whatever you want depending on your condition.

—SA