Unable to access MDB file using OleDbConnection

Kok Keong Chua

Hi,
I need help to resolve this problem:

I would like to access a MDB file and query some data from it, under the debug mode, Locals window, I'm able to see the data inside the reader object if i query for the whole table using the syntax as shown below:

using (OleDbConnection AccessConnection = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0; User Id=; Password=; Data Source=C:\PVCTData\Measurement_Result.mdb"))

{
     OleDbCommand cmd = new OleDbCommand("SELECT * FROM Results order by TestTimeDate", AccessConnection);
     AccessConnection.Open();
     OleDbDataReader reader;
      reader = cmd.ExecuteReader();
      MessageBox.Show(reader.GetValue(0).ToString());
      reader.Close();
      AccessConnection.Close();
       return sn;
}

however, if i just want to retrieve one record by using the query "SELECT top1 CellIDStr FROM Results order by TestTimeDate", the program will throw an exception:

exception    {"No data exists for the row/column."}
System.Exception {System.InvalidOperationException}

May i know what is the problem in my code? Thanks.

3 Replies

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Vulpes15y ago
Accepted answer
I'd use the ExecuteScalar() method to get a single value rather than use an OleDbDataReader:

using (OleDbConnection AccessConnection = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0; User Id=; Password=; Data Source=C:\PVCTData\Measurement_Result.mdb"))
{
OleDbCommand cmd = new OleDbCommand("SELECT top1 CellIDStr FROM Results order by TestTimeDate", AccessConnection);
AccessConnection.Open();
object obj = cmd.ExecuteScalar();
string value = "";
if (!Convert.IsDBNull(obj)) value = obj.ToString(); //make sure not null before applying ToString()
MessageBox.Show("The value returned is " + value);
}
return sn;
Kok Keong Chua15y ago
Thanks Vulpes, problem resolved after i use executeScalar().
Suthish Nair15y ago
try like this.. to avoid error

while(reader.Read())
{
MessageBox.Show(reader.GetString(0));
}