error in query string

using (SqlConnection con = new SqlConnection(exh_SQLHelper.GetConnectionString())) { string usernameId = "admin"; int exhId1 = Convert.ToInt16(Request.QueryString["id"]); if ((!IsPostBack) && (exhId1 != 0)) { string sql = "Select * from where showId=" + exhId1 +"and userName=" usernameId ;