MySQL深分页问题原理与三种解决方案-数据库

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1 深分页问题

1.1 创建表

CREATE TABLE `player` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `player_id` varchar(256) NOT NULL COMMENT '运动员编号',
  `player_name` varchar(256) NOT NULL COMMENT '运动员名称',
  `height` int(11) NOT NULL COMMENT '身高',
  `weight` int(11) NOT NULL COMMENT '体重',
  `game_performance` text COMMENT '最近一场比赛表现',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8

1.2 新增100万条数据

@SpringBootTest(classes = TestApplication.class)
@RunWith(SpringJUnit4ClassRunner.class)
public class PlayerServiceTest {

    @Resource
    private PlayerRepository playerRepository;

    @Test
    public void initBigData() {
        for (int i = 0; i < 1000000; i++) {
            PlayerEntity entity = new PlayerEntity();
            entity.setPlayerId(UUID.randomUUID().toString());
            entity.setPlayerName("球员_" + System.currentTimeMillis());
            entity.setWeight(150);
            entity.setHeight(188);
            entity.setGamePerformance("{\"runDistance\":8900.0,\"passSuccess\":80.12,\"scoreNum\":3}");
            playerRepository.insert(entity);
        }
    }
}

1.3 深分页语句

select * from player limit 990000,5

1.4 结果分析

查询耗时：1.233秒
本语句目标查询[990001-990005]五条数据
但是执行时需要排序[1-990005]数据
最终丢弃[1-990000]只返回[990001-990005]数据

2 深分页优化方案

2.1 方案一

我们可以从业务形态维度去解决，可以参考搜索引擎解决方案。因为ES也存在深分页问题，搜索引擎解决方案是在业务上会限制查询页数。因为页数越大，内容相关度越低，所以页数太大对业务价值不高。MySQL可以类比处理：

限制查询页数
限制全量导出
查询时要求带必要条件（时间范围、userId）

2.2 方案二

2.2.1 优化语句

select * from player a, (select id as tmpId from player limit 990000,5) b WHERE a.id = b.tmpId

2.2.2 执行计划

(1) 查看计划

explain select * from player a, (select id as tmpId from player limit 990000,5) b WHERE a.id = b.tmpId

(2) 执行顺序

id越大执行顺序越靠前
id相同则按照行数从上到下执行
本语句执行顺序如下图：

第一步和第二步表示执行子查询
第三步表示player表与子查询关联

(3) explain type

访问类型是重要分析指标：

(4) explain Extra

Extra表示执行计划扩展信息重点关注三个：

2.2.3 结果分析

查询耗时：0.5秒
原因是覆盖索引提升分页查询效率（只查询ID列）
覆盖索引含义是查询时索引列完全包含查询列
using index表示使用覆盖索引，性能提升

2.3 方案三

2.3.1 优化语句

select * from player where id > 990000 LIMIT 5

2.3.2 执行计划

(1) 查看计划

explain select * from player where id > 990000 LIMIT 5

(2) 结果分析

查询耗时：0.001秒
range表示索引范围搜索性能尚可

(3) 适用场景

不适用跳页场景
只适用【上一页】【下一页】场景

3 MyBatis

<mapper namespace="com.test.java.front.test.mysql.deep.page.repository.PlayerRepository">

	<resultMap id="BaseResultMap" type="com.test.java.front.test.mysql.deep.page.entity.PlayerEntity">
		<id column="id" jdbcType="BIGINT" property="id" />
		<result column="player_id" jdbcType="VARCHAR" property="playerId" />
		<result column="player_name" jdbcType="VARCHAR" property="playerName" />
		<result column="height" jdbcType="INTEGER" property="height" />
		<result column="weight" jdbcType="INTEGER" property="weight" />
		<result column="game_performance" jdbcType="LONGVARCHAR" property="gamePerformance" />
	</resultMap>

	<sql id="Base_Column_List">
		id, player_id, player_name, height, weight, game_performance
	</sql>

	<sql id="conditions">
		<where>
			<if test="playerId != null">
				and player_id = #{playerId,jdbcType=VARCHAR}
			</if>
		</where>
	</sql>

	<sql id="pager">
		<if test="skip != null and limit != null">
			limit #{skip}, #{limit}
		</if>
	</sql>

	<!-- 查询条数 -->
	<select id="selectPageCount" parameterType="com.test.java.front.test.mysql.deep.page.param.biz.PlayerQueryParam" resultType="java.lang.Long">
		select count(*) from player
		<include refid="conditions" />
	</select>

	<!-- 分页方式1：普通分页存在深分页问题 -->
	<!-- select * from player limit 990000,5 -->
	<select id="selectPager1" parameterType="com.test.java.front.test.mysql.deep.page.param.biz.PlayerQueryParam" resultMap="BaseResultMap">
		select
		<include refid="Base_Column_List" />
		from player
		<include refid="conditions" />
		<include refid="pager" />
	</select>

	<!-- 分页方式2：覆盖索引优化深分页问题 -->
	<!-- select * from player a, (select id as tmpId from player limit 990000,5) b where a.id = b.tmpId -->
	<select id="selectPager2" parameterType="com.test.java.front.test.mysql.deep.page.param.biz.PlayerQueryParam" resultMap="BaseResultMap">
		select
		<include refid="Base_Column_List" />
		from player a,
		(
		select id as tmpId from player
		<include refid="conditions" />
		<include refid="pager" />
		) b
		where a.id = b.tmpId
	</select>

	<!-- 分页方式3：Id分页不支持跳页 -->
	<!-- select * from player where id > 990000 limit 5 -->
	<select id="selectPager3" parameterType="com.test.java.front.test.mysql.deep.page.param.biz.PlayerQueryIdParam" resultMap="BaseResultMap">
		select
		<include refid="Base_Column_List" />
		<include refid="conditions" />
		from player where id > #{startId} limit #{pageSize}
	</select>
</mapper>