java怎么查询数据库-java教程

java查询数据库的方法：首先创建user和teacher数据库；然后将teacher表的【user_id】列与user表的id列建立一对多连接；接着向user数据表中添加数据，并按照条件查询user数据库数据；最后根据主表查询从表数据。

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java查询数据库的方法：

一、创建数据库

创建 user 数据库

创建 teacher 数据库

teacher表的user_id列与user表的id列建立一对多连接，user_id作为外键。

二、Java编程查询数据库

向user数据表中添加数据

    /**     * 添加数据     */    @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("数据添加成功！");            }else {                System.out.println("数据添加失败！");            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }finally{            JDBCUtils_V3.release(connection, pstmt, null);        }    }

按照条件查询user数据库数据

    /**     * 按照条件查询数据     */    @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);        }    }

一对多查询/根据主表user查询从表teacher数据

    /**     * 一对多查询     * 根据主表查询从表     */    @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("查询完成");        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }finally{            JDBCUtils_V3.release(conn, pstmt, rs);        }    }

一对多查询/根据从表查询主表

    /**     * 一对多查询     * 根据从表查询主表数据     */    @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, "钱田");            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);        }    }}

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