Java查詢數據庫

時間 2019-12-12

標籤 java 查詢數據庫欄目 Java 简体版

原文原文鏈接

建立數據庫

建立 user 數據庫git

建立 teacher 數據庫github

teacher表的user_id列與user表的id列創建一對多鏈接，user_id做爲外鍵。sql

Java編程查詢數據庫

向user數據表中添加數據

    /**
     * 添加數據
     */
    @Test
    public void addData() {
        Connection connection = null;
        PreparedStatement pstmt =null;
        try {
            connection = JDBCUtils_V3.getConnection();
            String sql = "insert into user values(null,?,?)";
            pstmt = connection.prepareStatement(sql);
            pstmt.setString(1, "wangxuan");
            pstmt.setString(2, "741852");
            int row = pstmt.executeUpdate();
            if (row>0) {
                System.out.println("數據添加成功！");
            }else {
                System.out.println("數據添加失敗！");
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            JDBCUtils_V3.release(connection, pstmt, null);
        }
    }

按照條件查詢user數據庫數據

    /**
     * 按照條件查詢數據
     */
    @Test
    public void selectTest() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs =null;
        try {
            conn = JDBCUtils_V3.getConnection();
            String sql = "select * from user where password = ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "123456");
            rs = pstmt.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3));
            }
//            System.out.println(rs);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            JDBCUtils_V3.release(conn, pstmt, rs);
        }
    }

一對多查詢/根據主表user查詢從表teacher數據

    /**
     * 一對多查詢
     * 根據主表查詢從表
     */
    @Test
    public void selectOnetoMore() {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils_V3.getConnection();
//            String sql = "select * from teacher where user_id = (select id from user where username =?) ";
            String sql = "select * from user,teacher where user.id = teacher.user_id ";
            pstmt = conn.prepareStatement(sql);
//            pstmt.setString(1, "wangxuan");
            rs = pstmt.executeQuery();
            while (rs.next()) {
//                System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3)+"---"+rs.getString(4));
                System.out.println(rs.getString(1)+"----"+rs.getString(2)+"---"+rs.getString(3)+"---"+rs.getString(4)+"----"+rs.getString(5)+"----"+rs.getString(6)+"----"+rs.getString(7));
            }
            System.out.println("查詢完成");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            JDBCUtils_V3.release(conn, pstmt, rs);
        }
    }

一對多查詢/根據從表查詢主表

    /**
     * 一對多查詢
     * 根據從表查詢主表數據
     */
    @Test
    public void selectMoretoOne() {
        Connection connection = null;
        PreparedStatement pstmtPreparedStatement = null;
        ResultSet rSet =null;
        try {
            connection = JDBCUtils_V3.getConnection();
            String sql = "select * from user where id = (select user_id from teacher where teacher=?)";
            pstmtPreparedStatement = connection.prepareStatement(sql);
            pstmtPreparedStatement.setString(1, "錢田");
            rSet = pstmtPreparedStatement.executeQuery();
            while (rSet.next()) {
                System.out.println(rSet.getString(1)+"----"+rSet.getString(2)+"---"+rSet.getString(3));
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            JDBCUtils_V3.release(connection, pstmtPreparedStatement, rSet);
        }
    }
}