Query is not returning results in MS Access with C#?

问题

So I have a relatively simple query, but it is not matching the full_name text field even though I can see the data is there and is an exact match?

I made sure to checkk the fullName parameter being passed in is the correct value. I couldn't find any documentation verifying if I needed the single quotes or not, but without it an error was thrown.

Anyone have any suggestions?

Code in question with the SQL statement?

    public static ObservableCollection<ShiftView> GetShifts(DateTime? start, DateTime? stop, string fullName, bool? closed)
    {
        ObservableCollection<ShiftView> shifts = new ObservableCollection<ShiftView>();

        // INFO: Not intended to retrieve a lot of records as there is no caching....
        OleDbCommand cmd = new OleDbCommand("SELECT profiles.profile_id, profiles.full_name, shifts.start, shifts.stop, shifts.start_log, shifts.stop_log, shifts.start_notes, shifts.stop_notes FROM shifts, profiles WHERE " + 
            (start.HasValue ? "(shifts.start>=@start) AND " : "") +  
            (stop.HasValue ? "(shifts.stop<=@stop) AND " : "") +
            (fullName != null ? "profile.full_name='@full_name' AND " : "") +
            (closed.HasValue ? "shifts.closed=@closed AND " : "") +
            "(shifts.profile_id=profiles.profile_id)"
            );

        if (start.HasValue)
            cmd.Parameters.AddWithValue("@start", start.Value.ToString());
        if (stop.HasValue)
            cmd.Parameters.AddWithValue("@stop", stop.Value.ToString());
        if (fullName != null)
            cmd.Parameters.AddWithValue("@full_name", fullName);
        if (closed.HasValue)
            cmd.Parameters.AddWithValue("@closed", closed);
        OleDbDataReader reader = Database.Read(cmd);

        DateTime? _stop, _stopLog;

        while(reader.Read())
        {
            Console.WriteLine("!");
            // shorthand form if's with ? does not work here.
            if (reader.IsDBNull(reader.GetOrdinal("stop")))
                _stop = null;
            else
                _stop = reader.GetDateTime(reader.GetOrdinal("stop"));

            if (reader.IsDBNull(reader.GetOrdinal("stop_log")))
                _stopLog = null;
            else
                _stopLog = reader.GetDateTime(reader.GetOrdinal("stop_log"));

            shifts.Add(new ShiftView(
                reader.GetString(reader.GetOrdinal("profile_id")), 
                reader.GetString(reader.GetOrdinal("full_name")),
                reader.GetDateTime(reader.GetOrdinal("start")),
                _stop,
                reader.GetDateTime(reader.GetOrdinal("start_log")),
                _stopLog,
                reader.GetString(reader.GetOrdinal("start_notes")),
                reader.GetString(reader.GetOrdinal("stop_notes"))
                ));
        }

        return shifts;
    }

The above code gets called from this button press:

    private void ShowStatsButton_Click(object sender, RoutedEventArgs e)
    {
        DateTime? start = StartDatePicker.SelectedDate;
        DateTime? stop = StopDatePicker.SelectedDate;
        string name = NameComboBox.Text;

        if (name.Equals("Everyone"))
            name = null;

        if (stop.HasValue)
            stop = stop.Value.AddDays(1);

        StatsGridView.ItemsSource = Shift.GetShifts(start, stop, name, true);
    }

This filters the date range and if there is a full name. I ensure there is a valid value for name.

回答1:

I think that the problem is in here, you need to remove '' from full_name line:

OleDbCommand cmd = new OleDbCommand("SELECT profiles.profile_id, profiles.full_name, shifts.start, shifts.stop, shifts.start_log, shifts.stop_log, shifts.start_notes, shifts.stop_notes FROM shifts, profiles WHERE " + 
            (start.HasValue ? "(shifts.start>=@start) AND " : "") +  
            (stop.HasValue ? "(shifts.stop<=@stop) AND " : "") +
            (fullName != null ? "profile.full_name='@full_name' AND " : "") +  <-- remove '' from '@full_name'
            (closed.HasValue ? "shifts.closed=@closed AND " : "") +
            "(shifts.profile_id=profiles.profile_id)"
            );

and do this:

OleDbCommand cmd = new OleDbCommand("SELECT profiles.profile_id, profiles.full_name, shifts.start, shifts.stop, shifts.start_log, shifts.stop_log, shifts.start_notes, shifts.stop_notes FROM shifts, profiles WHERE " + 
            (start.HasValue ? "(shifts.start>=@start) AND " : "") +  
            (stop.HasValue ? "(shifts.stop<=@stop) AND " : "") +
            (fullName != null ? "profile.full_name=@full_name AND " : "") +
            (closed.HasValue ? "shifts.closed=@closed AND " : "") +
            "(shifts.profile_id=profiles.profile_id)"
            );

I hope this help

回答2:

It turns out that adding in the table name was the cause of the problem. Why this is the case, is uncertain and I will follow up with another question specific to that.

So the solution I eventually went with to change the following:

    OleDbCommand cmd = new OleDbCommand("SELECT profiles.profile_id, profiles.full_name, shifts.start, shifts.stop, shifts.start_log, shifts.stop_log, shifts.start_notes, shifts.stop_notes FROM shifts, profiles WHERE " + 
        (start.HasValue ? "(shifts.start>=@start) AND " : "") +  
        (stop.HasValue ? "(shifts.stop<=@stop) AND " : "") +
        (fullName != null ? "profile.full_name='@full_name' AND " : "") + // this is where the problem is
        (closed.HasValue ? "shifts.closed=@closed AND " : "") +
        "(shifts.profile_id=profiles.profile_id)"
        );

and change it to:

        (fullName != null ? "full_name=@full_name AND " : "") + // Notice I removed the table name and just straight referenced the field.

EDIT:

I updated the above correct line to remove single quotes, that I accidentally left in copy and pasting (numero uno coding mistake!).

I also discovered why I kept getting an error staring at it for hours. Turns out, the table is called "profiles", not "profile" and therefore when I removed the table name it worked!

So an alternative solution is:

(fullName != null ? "profiles.full_name=@full_name AND " : "") 

Silly, I know. Feel stupid now.

来源：https://stackoverflow.com/questions/25209593/query-is-not-returning-results-in-ms-access-with-c