Nell'esempio di sotto, uso un SqlDataSource e non scrivo una riga di codice; e anche questo va.

codice:
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" PagerSettings-Mode="NumericFirstLast" EnableViewState="False" AllowSorting="True" EnablePersistedSelection="True" AutoGenerateColumns="False" DataKeyNames="id" DataSourceID="SqlDataSource1" AutoGenerateSelectButton="True" SortedAscendingCellStyle-BackColor="#FFFF99" SortedDescendingCellStyle-BackColor="#00FF99">

	<PagerSettings Mode="NumericFirstLast"></PagerSettings>

	<SelectedRowStyle BackColor="#DDDFBD" />
	<Columns>
		<asp:BoundField DataField="id" HeaderText="id" ReadOnly="True" SortExpression="id" />
		<asp:BoundField DataField="stringa" HeaderText="stringa" SortExpression="stringa" />
		<asp:BoundField DataField="numero" HeaderText="numero" SortExpression="numero" />
		<asp:BoundField DataField="data" HeaderText="data" SortExpression="data" />
		<asp:BoundField DataField="data_stringa" HeaderText="data_stringa" SortExpression="data_stringa" />
		<asp:BoundField DataField="data_data" HeaderText="data_data" SortExpression="data_data" />
	</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="server=localhost;User Id=test;password=0000;Persist Security Info=True;database=test" ProviderName="MySql.Data.MySqlClient" SelectCommand="SELECT *, str_to_date(data_stringa, '%d/%m/%Y') as data_data from table1"></asp:SqlDataSource>