SELECT / ResultSet

import dao.BankDAO;
import db.DBConnection;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Scanner;

public class BankApp {
    public static void main(String[] args) {
        //이거 BR로도 만들 수 있다
        Scanner sc = new Scanner(System.in);

        System.out.print("삭제할 계좌번호를 입력해주세요 : ");
        int number = sc.nextInt();

        //DAO한테 위임
        BankDAO dao = new BankDAO();

        //결과를 int로 안받으면 잘 됐는지 안됐는지 고객이 알 수가 없음
        int result = dao.deleteByNumber(number);

        if (result == 1) {
            System.out.println("삭제 성공했습니다");
        } else {
            System.out.println("삭제 실패했습니다");
        }
    }
}

package dao;

import db.DBConnection;
import model.Account;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

public class BankDAO {

    public int deleteByNumber(int number) {
        Connection conn = DBConnection.getInstance();
        try {
            String sql = "delete from account_tb where number = ?";

            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1,number);
            int num = pstmt.executeUpdate();
            return num;

        } catch (Exception e) {
            e.printStackTrace();
        }
        return -1;
    }

    public int insert(String password, int balance) {
        Connection conn = DBConnection.getInstance();
        try {
            String sql = "insert into account_tb(password, balance, created_at) values(?, ?, now())";

            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setString(1,password);
            pstmt.setInt(2,balance);
            int num = pstmt.executeUpdate();
            return num;

        } catch (Exception e) {
            e.printStackTrace();
        }
        return -1;
    }

    public int updateByNumber(int balance, int number) {
        Connection conn = DBConnection.getInstance();
        try {
            String sql = "update account_tb set balance = ? where number = ?";

            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1,balance);
            pstmt.setInt(2,number);
            int num = pstmt.executeUpdate();
            return num;

        } catch (Exception e) {
            e.printStackTrace();
        }
        return -1;

    }

    //where에 number가 걸릴거다.
    public Account selectByNumber(int number){
        Connection conn = DBConnection.getInstance();
        try {
            String sql = "select * from account_tb where number = ?";
            PreparedStatement pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, number);

            ResultSet rs = pstmt.executeQuery();

            boolean isRow = rs.next(); // 커서 한칸 내리기

            if(isRow){
                Account account = new Account(
                        rs.getInt("number"),
                        rs.getString("password"),
                        rs.getInt("balance"),
                        rs.getTimestamp("created_at")
                );
                return account;
            }
        }catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }

    public List<Account> selectAll() {
        Connection conn = DBConnection.getInstance();
        try {
            String sql = "select * from account_tb order by number desc";
            PreparedStatement pstmt = conn.prepareStatement(sql);

            ResultSet rs = pstmt.executeQuery();

            List<Account> accountList = new ArrayList<>();
            while (rs.next()){
                Account account = new Account(
                        rs.getInt("number"),
                        rs.getString("password"),
                        rs.getInt("balance"),
                        rs.getTimestamp("created_at")
                );
                accountList.add(account);
            }
            return accountList;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

}

package model;

import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.sql.Timestamp;

@Getter
@AllArgsConstructor
@ToString
public class Account {
    private int number;
    private String password;
    private int balance;
    private Timestamp createdAt;

}