获取一个SQL表中的数据计数与另一个SQL表的关系，并在java中使用它

Question

I have 2 database tables for my program: GameInfo and Characters. How this works is that a Game has 4 maps with different names and each character added to the game must be assigned any of the 4 maps. Now I have the sql statement which returns a result set named "Expr1001, of the number of characters on each map. I then need to add this information to a jTable and link up the corresponding amount of each characterson a map, with the mapname.

My ResultSet with the query which returns the amount of characters on each map:

ResultSet qs = dbm.queryDatabase("SELECT Expr1001 FROM (SELECT GameInfo.mapname, SUM(IIF(Map = GameInfo.mapname,1,0)) FROM (SELECT * FROM [Character] INNER JOIN Player ON Character.PlayerID=Player.[ID])  AS A RIGHT JOIN GameInfo ON A.Character.map = GameInfo.mapname GROUP BY GameInfo.mapname)  AS [%$##@_Alias]");

The whole method which gets the Game Info from the database from the GameInfo table, which comprises of a GameID and MapName only.

 public Game[] getGameInfo(){
       Game[] arr = null; //Creates an array of Games


    try { //getting list from database
        ResultSet rs = dbm.queryDatabase("Select Count(GameID) as NumGames from GameInfo" );
        //While there are still more rows to read from the database.
        rs.next();
        int count = rs.getInt("NumGames");
        arr = new Game[count];
        String sql = "Select * from GameInfo";
       // System.out.println(sql);

        rs = dbm.queryDatabase(sql);
        //Take the info from the current row
        //Add the info to the array
         ResultSet qs = dbm.queryDatabase("SELECT Expr1001 FROM (SELECT GameInfo.mapname, SUM(IIF(Map = GameInfo.mapname,1,0)) FROM (SELECT * FROM [Character] INNER JOIN Player ON Character.PlayerID=Player.[ID])  AS A RIGHT JOIN GameInfo ON A.Character.map = GameInfo.mapname GROUP BY GameInfo.mapname)  AS [%$##@_Alias]");
        for(int i = 0; rs.next(); i++){

            arr[i] = new Game(
                    rs.getInt("GameInfo.GameID"), 
                    rs.getString("GameInfo.mapname"), 
                 qs.getInt(i));
        }//Creates a Game from the currently selected info


    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, "Failed to get Games");
        e.printStackTrace();
    }
    return arr;
}

}

The data is then added to the jTable which is on a Panel in the GameInfoPanel class:

 public void refreshTable() {
    //remove old stuff
    refreshing = true;

    Game[] arr = gim.getGameInfo();
    DefaultTableModel model = (DefaultTableModel) GameInfoTable.getModel();
    while (model.getRowCount() > 0) {
        model.removeRow(0);

    }
    for (int i = 0; i < arr.length; i++) {
        model.addRow(new Object[]{
            arr[i].getNumberOfCharacters(),
           arr[i].getID(),
            arr[i].getMapName()});
    }
    refreshing = false;

    //load new data from database using manager
}

I keep getting the error which points to the ResultSet qs line: "user lacks privilege or object not found: A.CHARACTER.MAP" when I try and run the program even though when I copy this statement into Microsoft Access and run it, it's fine.

Help please! Thanks.

(I am still at school so not really a genius on this at all so please have mercy if I've done some stupid things)

Answer 1

Don't run a select count(*) first to get the number of games for allocating an array. Build you result in a List , which will auto-expand as needed. You can always convert the list to an array later, if needed.

Don't run two queries when one can do the job, especially when you already join to the table in question.

Your SQL is unreadable, so here it is in a more readable format:

String sql = "SELECT Expr1001" +
              " FROM (SELECT GameInfo.mapname" +
                          ", SUM(IIF(Map = GameInfo.mapname,1,0))" +
                      " FROM (SELECT *" +
                              " FROM [Character]" +
                             " INNER JOIN Player ON Character.PlayerID=Player.[ID]" +
                            ")  AS A" +
                     " RIGHT JOIN GameInfo ON A.Character.map = GameInfo.mapname" +
                     " GROUP BY GameInfo.mapname" +
                    ")  AS [%$##@_Alias]";

The outer query does nothing. Get rid of it.
Don't SELECT * . Select the columns you want, ie Character.map .
Since you want GameID , add it to the GROUP BY .
Specify an alias for the SUM value.

public Game[] getGameInfo(){
    String sql = " SELECT GameInfo.GameID" +
                       ", GameInfo.mapname" +
                       ", SUM(IIF(C.map = GameInfo.mapname,1,0)) AS CharacterCount" +
                   " FROM ( SELECT Character.map" +
                            " FROM [Character]" +
                            " JOIN Player ON Player.[ID] = Character.PlayerID" +
                         ") C" +
                  " RIGHT JOIN GameInfo ON GameInfo.mapname = C.map" +
                  " GROUP BY GameInfo.GameID" +
                          ", GameInfo.mapname";
    try (ResultSet rs = dbm.queryDatabase(sql)) {
        List<Game> games = new ArrayList<>();
        while (rs.next())
            games.add(new Game(rs.getInt("GameID"),
                               rs.getString("mapname"),
                               rs.getInt("CharacterCount")));
        return games.toArray(new Game[games.size()]);
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, "Failed to get Games");
        e.printStackTrace();
        return null;
    }
}