I do not know why do not get data back - Ado.net

Question

My sqlQuery = string sql = "SELECT StoreType from location where locationId in (@pRowValue) order by region, district, locationId";

This is my code:

string storeNum = "";

foreach (DataRow row in dt.Rows)

{

storeNum += row["store"] + ",";

//storeNum += string.Format(@"'{0}',", row["store"]);

}

storeNum = storeNum.Remove(storeNum.LastIndexOf(','));

SqlDataAdapter da = new SqlDataAdapter(sql, con);

da.SelectCommand.Parameters.AddWithValue("@pRowValue", storeNum);

da.Fill(dtStoreType);

but I do not get any records back?