I would use this function:
OleDbConnection con = new OleDbConnection(@"yourConString");
OleDbCommand cmd = new OleDbCommand("SELECT MAX(Mileage) - MIN(Mileage), SUM(Litres) FROM Store WHERE PlateNo = @PlateNo AND Filldate BETWEEN @StartDate AND @EndDate",conEzstock);
cmd.Parameters.AddWithValue("@PlateNo", 5487844);
cmd.Parameters.AddWithValue("@StartDate", new DateTime(2011,8,1));
cmd.Parameters.AddWithValue("@EndDate", new DateTime(2011,8,3));
conEzstock.Open();
OleDbDataReader dbr = cmd.ExecuteReader();
int mileage;
double litresUsed;
while (dbr.Read())
{
mileage = (int)dbr[0];
litresUsed = (double)dbr[1];
}
dbr.Close();
con.Close();
Hope this helps