排行榜-SQL查询/ JDBC问题

Question

I currently have a very basic app that interacts with a database (Using netbeans and the jdbc) so that you can add teams, players and scores. I now need to be able to display items from each table together in a League Table/Team (With players) Table etc etc.

My question is how do I go about retrieving the information from the tables and how do I display it, I am literally clueless as to how I should go about it. I'm assuming I need to do a Join or Select statement (I'm a complete SQL novice) and then use a loop to select each table entry and display it in a table somehow?

The only current working features I have are adding to the database, IE add a new team add a new player etc, displaying what is in the tables on the form is where I am stumped.

Any tips or help is much appreciated.

The code I am currently using is this; (I still need to implement a score table and adding records to that, I also created the datbase using the GUI and so have no foreign keys set, is there a way to do this WITHIN netbeans as I have no "Create Table" code anywhere.

package football.game;
/*import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;*/
import football.game.DBconnection;
import java.sql.*;


/**
 *
 * @author Steffan Caine
 */
public class SportsConnection extends DBconnection {

public SportsConnection(final String dbName)
{
    this.connectDatabase(dbName);
}

public void insertPlayer(final Integer PLAYERNUM,
        final String PLAYERNAME, final String PLAYERPOS, final Integer TEAMNUM)
{
    final String insertStmt = "INSERT INTO APP.PLAYERS (PLAYERNUM, PLAYERNAME, PLAYER_POS, TEAM_ID) VALUES (?,?, ?, ?)";
    try
    {
        PreparedStatement pstmt = getConnection().prepareStatement(insertStmt);

        pstmt.setInt(1, PLAYERNUM);
        pstmt.setString(2, PLAYERNAME);
        pstmt.setString(3, PLAYERPOS);
        pstmt.setInt(4, TEAMNUM);
        pstmt.executeUpdate();
    }
    catch (SQLException sqle)
    {
        System.out.println("Exception when inserting player record: " + sqle.toString());
    }
}

public void insertTeam(final String NAME, final String MANAGER, final int ID)
{
    final String insertStmt = "INSERT INTO APP.TEAMS (TEAMNAME, MANAGER, TEAM_ID) VALUES (?,?, ?)";
    try
    {
        PreparedStatement pstmt = getConnection().prepareStatement(insertStmt);

        pstmt.setString(1, NAME);
        pstmt.setString(2, MANAGER);
        pstmt.setInt(3, ID);
        pstmt.executeUpdate();
    }
    catch (SQLException sqle)
    {
        System.out.println("Exception when inserting team record: " + sqle.toString());
    }
}

 public void printAllRecords()
{
    this.setQuery(retrieveQuery);
    this.runQuery();
    ResultSet output = this.getResultSet();
    try
    {
    if (null != output)
    {
        while(output.next())
        {

            String PLAYERNUM = output.getString(1);
            String PLAYERNAME = output.getString(2);

            System.out.println (PLAYERNUM + "\n" + PLAYERNAME + "\n");

        }
    }
    }
    catch (SQLException sqle)
    {
        System.out.println("Exception when printing all students: " + sqle.toString());
    }

}

}

The "retrieveQuery" currently returns an error message, any help getting that part to work would be great as printing the records out in a console would add some much needed (If basic) functionality.

I also have classes for each form (AddPlayer/AddTeam/Navigation) but I am not using constructors to populate the database I am instead using Methods located in a Main class, is this a bad way to go about things as I am not using "Objects" as such?

Thanks.

Answer 1

I see three tables: PLAYER, TEAM, and LEAGUE.

A TEAM has many PLAYERs; a LEAGUE has many TEAMs. These should be one-to-many relationships, so you'll have foreign keys. Here's an example:

CREATE TABLE PLAYER (
    int id not null auto increment,
    first_name varchar(80),
    last_name varchar(80),
    int team_id,
    primary key(id),
    foreign key(team_id) references TEAM(id)
);

CREATE TABLE TEAM (
    int id not null auto increment,
    name varchar(80),
    primary key(id)
);

So you might have Java classes like this:

package model;

public class Player {
    private Integer id,
    private String name;
// ctors, getters, etc.
}

public class Team {
    private Integer id,
    private String name,
    List<Player> players;
// ctors, getters, etc.
}

You'll have a persistence layer that will have all your SQL in it:

package persistence;

public interface PlayerDao {
    Player find(Integer id);
    List<Player> find();
    Integer save(Player p);
    void update(Player p);
    void delete(Player p);
}

Here's a sample implementation for PlayerDao:

package persistence; 

public class PlayerDaoImpl implements PlayerDao {
    private static final String SELECT_ALL = "SELECT id, name FROM PLAYER ";
    private static final String SELECT_BY_ID = SELECT_ALL + "WHERE id = ?";

    private Connection connection;

    public PlayerDaoImpl(Connection connection) {
        this.connection = connection;
    }

    public Player find(Integer id) {
        Player p = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            ps = this.connection.prepareStatement(SELECT_BY_ID);
            ps.setInteger(1, id);
            rs = ps.executeQuery();
            while (rs.next()) {
                Integer pid = rs.getInteger("id");
                String name = rs.getString("name");
                p = new Player(id, name);
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        } finally {
            DatabaseUtils.close(rs);
            DatabaseUtils.close(ps);
        }
        return p;
    }
}

Printing records in consoles or user interfaces would indeed be useful, but that should be done by different classes in different packages. Have a view tier that handles that stuff. Classes should do one thing well. You should think about layering your applications appropriately.