Auto generate No while Import data from Excel to Database using C# and VB.Net in ASP.Net

Try below Code

 In Sql

Create proc [dbo].[SP_Name]
as
select ISNULL (MAX(AdmissionNo),0)+1 from TableName
return

 In Class File

 public DataSet GetOrderIDUniqueMax()
        {
            DataSet ds = new DataSet();
            cmd = new SqlCommand("SP_Name", obj_con.Obj_ConLink);
            cmd.CommandType = CommandType.StoredProcedure;
            da = new SqlDataAdapter(cmd);
            da.Fill(ds);
            return ds;
        }

 Code Behind

ClassName ObCls = new ClassName
  public void ORderIDGenearate()
        {
            ds = obCls.GetOrderIDUniqueMax();
            lblMaxIdForOrder.Text = ds.Tables[0].Rows[0][0].ToString();
        }

  _AdmissionNo = "R-" + lblMaxIdForOrder.Text;

Ouput id

R-0001