StringBuilder strb = new StringBuilder();
foreach(DataRow dr in dt.Rows)
{
    if(strb.Length > 0)
    {
        strb.Append("#");
    }
    strb.Append(string.format("{0},{1},{2}", dr["bh"].ToString(), dr["name"].ToString(), "Zy"));
}
string result = strb.ToString();

------解决方案--------------------
C# code
SqlConnection conn = ......;
conn.Open();
SqlDataAdapter ada = new SqlDataAdapter("select bh, name from v", conn);
var dtbl = new DataTable();
ada.Fill(dtbl);

var result = string.Join("#", Array.ConvertAll(dtbl.Select(), v1 => string.Join(",", v1.ItemArray) + ",Zy"));