1
我在我的網頁此代碼:讀取MySql數據庫的平均值。 C#ASP.NET
protected void Page_Load(object sender, EventArgs e)
{
conn.Open();
string selectQuery = @"SELECT AVG(odometer_reading),truck_id FROM
inspection WHERE date BETWEEN '2015-12-01' AND '2016-06-01'
GROUP BY truck_id";
MySqlCommand cmd = new MySqlCommand(selectQuery, conn);
MySqlDataReader reader = cmd.ExecuteReader();
foreach (DbDataRecord rowData in reader)
{
populateTable(rowData);
}
}
private void populateTable (DbDataRecord rowData)
{
TableRow tr = new TableRow();
TableCell cell1 = new TableCell();
cell1.Text = rowData.GetString(rowData.GetOrdinal("AVG(odometer_reading)")).ToString();
tr.Cells.Add(cell1);// Error
TableCell cell2 = new TableCell();
cell2.Text = rowData.GetString(rowData.GetOrdinal("truck_id")).ToString();
tr.Cells.Add(cell2);
tbl_TruckEfficiency.Rows.Add(tr);
}
我收到的Unable to cast object of type 'System.Double' to type 'System.String'.
的錯誤可能是。這是什麼原因。
或者
是否有其他方式來獲得AVG(odometer_reading)
得到它cell1.text
考慮其數據類型,以避免錯誤。謝謝!
先給'AVG(odometer_reading)'的別名例如'AVG(odometer_reading)作爲AverageRead'並使用此別名獲取數據 – Prabhat
rowData.GetOrdinal將獲取列位置而不是值。嘗試在實現別名後使用GetDecimal或GetDouble,如[suprabhat]所示(http://stackoverflow.com/users/3513848/suprabhat-biswal) –
我的'odometer_reading'具有一個varchar數據類型,意味着它是一個帶有數字值的字符串,所以我做了這個'object value = Convert.ToDouble(rowData.GetString(rowData.GetOrdinal(「AverageOdo」)))。ToString(); cell1.Text = value.ToString();'相同的結果 –