使用C＃将DataTable发送到Access数据库

Question

I have table (about 250k rows) in Access db with date, time and name (other columns are irrelevant for this problem). I need to get just first (or last) date/time for name value and send it to new table.

I have tried SQL statement but for large number of rows it is too slow. here: Access SQL to return only first or last occurence by date

I also tried read data from db to DataTable, looping through and deleting rows that I don't want, but I'm not able to send this edited DataTable back to db. Similar to this: How do I insert a datatable into Microsoft Access?

using(OleDbConnection con = new OleDbConnection(ConnectionString))
{
    SQL = "Select * From OriginalTable";
    var adapter = new OleDbDataAdapter();
    adapter.SelectCommand = new OleDbCommand(SQL, con);
    var cbr = new OleDbCommandBuilder(adapter);

    try
    {
        con.Open();

        DataTable dtFilter = new DataTable();
        adapter.Fill(dtFilter);
        string id = dtFilter.Rows[dtFilter.Rows.Count - 1][4].ToString();
        for(int i = dtFilter.Rows.Count - 2; i >= 0; i--)
        {
            DataRow dr = dtFilter.Rows[i];
            if(dtFilter.Rows[i][4].ToString() == id)
            {
                dr.Delete();
            }
            else
            {
                id = dtFilter.Rows[i][4].ToString();
            }
        }
        dtFilter.AcceptChanges(); // DataTable looks as I want
        adapter.Update(dtFilter); // Returns 0 
    }
    catch(OleDbException ex)
    {
        MessageBox.Show(ex.Message, "OledbException Error");
    }
    catch(Exception x)
    {
        MessageBox.Show(x.Message, "Exception Error");
    }
}

I expect to export dtFilter to Access db. Why it returns 0?

I'm open for SQL statement as long as it is fast.

UPDATE: SQL Statement used for selecting first or last entry

SELECT DISTINCT 
    cdate(Format(t.DateOS + t.TimeOS, 'dd.MM.yyyy HH:mm:ss')) AS DateTimeOS, 
    cdate(Format(t.DateOS, 'dd.MM.yyyy ')) AS DateOS, 
    cdate(Format(t.TimeOS, 'HH:mm:ss')) AS TimeOS, 
    t.EP AS EP, t.ID AS ID 
FROM TestFirstLast AS t 
WHERE t.EP = 'L100' 
    AND (((t.DateOS + t.TimeOS) > #1/1/2016 12:00:00 AM# AND (t.DateOS + t.TimeOS) <= #3/1/2016 12:00:00 AM#)) 
    AND NOT EXISTS(SELECT 1 FROM TestFirstLast AS t2 WHERE t2.EP = t.EP AND t2.ID = t.ID AND (t2.DateOS < t.DateOS OR t2.DateOS = t.DateOS AND t2.TimeOS < t.TimeOS))

GOOD SOLUTION: I found good description of problem and solution here

Answer 1

To use the .Update method, you have to provide an update SQL command.

The OleDbDataAdapter provides

• InsertCommand
• UpdateCommand
• DeleteCommand

If you are not setting the corresponding command, the DataAdapter does not know what to do with your data.

Have a look at OleDbDataAdapter Class