分页查询

思考：为什么要分页?

• 减少数据的处理量

1、使用Limit分页

语法:select * from user limit startIndex,pageSize;

select * from user limit 3;#[0,n]

使用Mybatis实现分页，核心SQL

• 接口

    /**
     * 分页查询
     * @return
     */
    List<User> getUserByLimt(Map<String,Integer> map);

 

• Mapper.xml

 <!--分页实现查询 -->
    <select id="getUserByLimt" parameterType="map" resultMap="UserMap">
        select * from mybatis.user  limit #{startIndex},#{pageSize}
    </select>

• 测试

    public void getUserByLimt(){
        SqlSession sqlsession = MybatisUtil.getSqlsession();
        UserMapper mapper = sqlsession.getMapper(UserMapper.class);
        HashMap<String, Integer> map = new HashMap<String, Integer>();
        map.put("startIndex",0);
        map.put("pageSize",3);
        List<User> userByLimt = mapper.getUserByLimt(map);
        for (User user : userByLimt) {
            System.out.println(user);
        }
    }

2、RowBounds分页

不在使用SQL实现分页

• 接口

/**
     *
     * @return
     */
    List<User> getUserByRowBounds();

• Mapper.xml

<!--分页实现查询 -->
    <select id="getUserByRowBounds" resultMap="UserMap">
        select * from mybatis.user
    </select>

• 测试

 public void getUserByRowBounds(){
        SqlSession sqlsession = MybatisUtil.getSqlsession();
        //RowBounds实现
        RowBounds rowBounds = new RowBounds(1, 2);
        //通过java层面实现分页
        List<User> list = sqlsession.selectList("com.dao.UserMapper.getUserByRowBounds",null,rowBounds);
        for (User user : list) {
            System.out.println(user);
        }
        //关闭sqlSession
        sqlsession.close();
    }

3、Mybatis分页插件