How to bind two column values in dropdownlist

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SQL

.NET

my table has three columns productid,productname,price

In dropdownlist i want display all productname-price from database.

in dropdown i need like this below

iphone-15000
oneplus-2000

all in gridview column.

What I have tried:

protected void gvdetail_RowDataBound(object sender, GridViewRowEventArgs e)
     {
         SqlConnection con1 = new SqlConnection(@"user id=sa;password=ssa;database=Mohan;data source=PCTH101\PCTH101");
         if (e.Row.RowType == DataControlRowType.DataRow)
         {
           con1.Open();
             var ddl = (DropDownList)e.Row.FindControl("DropDownList3");
             int productid = Convert.ToInt32(e.Row.Cells[0].Text);
             SqlCommand cmd = new SqlCommand("SELECT * from productinfo1", con1);
             SqlDataAdapter da = new SqlDataAdapter(cmd);
             DataSet ds = new DataSet();
             da.Fill(ds);
             con1.Close();
             ddl.DataSource = ds;
             ddl.DataTextField = "productname-price";
          //   ddl.DataTextField = "price";
             ddl.DataValueField = "productid";
             ddl.DataBind();
             ddl.Items.Insert(0, new ListItem("--Select--", "0"));
         }

     }