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一文读懂 MySQL Explain 执行计划

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时间：2023-01-18 16:54:02 402浏览收藏

在数据库实战开发的过程中，我们经常会遇到一些这样那样的问题，然后要卡好半天，等问题解决了才发现原来一些细节知识点还是没有掌握好。今天golang学习网就整理分享《一文读懂 MySQL Explain 执行计划》，聊聊MySQL，希望可以帮助到正在努力赚钱的你。

一、前言

上周老周的一个好朋友让我出一篇教你读懂 SQL 执行计划，和我另一位读者反馈的面试题如何排查慢 SQL 的强相关，索性先出一篇一文读懂 MySQL Explain 执行计划。Explain 执行计划你一定得会看，不然你简历上就别去写什么你会 SQL 调优，不然面试官会觉得，Explain 执行计划你都不会看，那你还 SQL 调啥优啊？SQL 调你吧？？？开个小玩笑，玩笑归玩笑，重要是真的重要！！！

二、Explain 执行计划是什么？

什么是执行计划？简而言之，就是 SQL 在数据库中执行时的表现情况，通常用于 SQL 性能分析、优化和加锁分析等场景，执行过程会在 MySQL 查询过程中由解析器，预处理器和查询优化器共同生成。在 MySQL 中使用 explain 关键字来查看。

2.1 执行计划有什么用？

它可以用来分析 SQL 语句和表结构的性能瓶颈

关联查询的执行顺序
查询操作的操作类型
哪些索引可以被命中
哪些索引实际被命中
每张表有多少记录参与查询
...

2.2 MySQL 执行过程

如上图所示，MySQL 数据库由 Server 层和 Engine 层组成：

Server 层有 SQL 分析器、SQL优化器、SQL 执行器，用于负责 SQL 语句的具体执行过程；
Engine 层负责存储具体的数据，如最常使用的 MyISAM、InnoDB 存储引擎，还有用于在内存中存储临时结果集的 TempTable 引擎。

SQL 优化器会分析所有可能的执行计划，选择成本最低的执行，这种优化器称之为：CBO（Cost-based Optimizer，基于成本的优化器）。

而在 MySQL 中，一条 SQL 的计算成本计算如下所示：

Cost = Server Cost + Engine Cost
= CPU Cost + IO Cost

其中，CPU Cost 表示计算的开销，比如索引键值的比较、记录值的比较、结果集的排序等这些操作都在 Server 层完成；

IO Cost 表示引擎层 IO 的开销，MySQL 8.0 可以通过区分一张表的数据是否在内存中，分别计算读取内存 IO 开销以及读取磁盘 IO 的开销。

数据库 mysql 下的表 server_cost、engine_cost 则记录了对于各种成本的计算，如：

表 server_cost 记录了 Server 层优化器各种操作的成本，这里面包括了所有 CPU Cost，其具体含义如下：

CREATE TABLE `user` (
    `id` INT (11) NOT NULL AUTO_INCREMENT,
    `name` VARCHAR (20) DEFAULT NULL COMMENT "用户名",
    PRIMARY KEY (`id`)
) ENGINE = INNODB DEFAULT CHARSET = utf8mb4 COMMENT = "用户表";

CREATE TABLE `user_robot_relate` (
    `id` INT (11) NOT NULL AUTO_INCREMENT,
    `user_id` INT (11) NOT NULL COMMENT "用户id",
    `robot_id` INT (11) NOT NULL COMMENT "机器人id",
    PRIMARY KEY (`id`), 
    KEY `idx_user_id` (`user_id`), 
    KEY `idx_robot_id` (`robot_id`)
) ENGINE = INNODB DEFAULT CHARSET = utf8mb4 COMMENT = "用户与机器人表";

CREATE TABLE `robot` (
    `id` INT (11) NOT NULL AUTO_INCREMENT,
    `name` VARCHAR ( 20 ) DEFAULT NULL COMMENT "机器人名",
    PRIMARY KEY (`id`)
) ENGINE = INNODB DEFAULT CHARSET = utf8mb4 COMMENT = "机器人表";

INSERT INTO user VALUES (1, 'riemann');
INSERT INTO user VALUES (2, 'andy');

INSERT INTO user_robot_relate VALUES (1, 1, 1);
INSERT INTO user_robot_relate VALUES (2, 1, 2);
INSERT INTO user_robot_relate VALUES (3, 2, 3);

INSERT INTO robot VALUES (1, '小白鲸');
INSERT INTO robot VALUES (2, '扫地机');
INSERT INTO robot VALUES (3, '扫拖一体机');

我们创建三张表 user、user_robot_relate、robot，表之间的关系 user.id = user_robot_relate.user_id AND user_robot_relate.robot_id = robot.id。

先来看下我的 MySQL 版本，是 5.7.37 的。

接着我们看一下执行计划有哪些字段，先看个整体的，让大家有个大概的认识后，我们再逐一去详解分析。

explain 执行后输出的结果集包含 12 列，分别是 id、select_type、table、partitions、type、possible_keys、key、key_len、ref、rows、filtered 和 Extra，下面对这些字段进行解释。

mysql> EXPLAIN SELECT * FROM user u WHERE u.id = (SELECT ur.user_id FROM user_robot_relate ur WHERE ur.robot_id = (SELECT r.id FROM robot r WHERE r.name = '扫地机'));
+----+-------------+-------+------------+------+--------------------------+------+---------+------+------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys            | key  | key_len | ref  | rows | filtered | Extra                                              |
+----+-------------+-------+------------+------+--------------------------+------+---------+------+------+----------+----------------------------------------------------+
|  1 | SIMPLE      | ur    | NULL       | ALL  | idx_user_id,idx_robot_id | NULL | NULL    | NULL |    3 |   100.00 | NULL                                               |
|  1 | SIMPLE      | u     | NULL       | ALL  | PRIMARY                  | NULL | NULL    | NULL |    2 |    50.00 | Using where; Using join buffer (Block Nested Loop) |
|  1 | SIMPLE      | r     | NULL       | ALL  | PRIMARY                  | NULL | NULL    | NULL |    3 |    50.00 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+------+--------------------------+------+---------+------+------+----------+----------------------------------------------------+

3.1.2 id 不同

如果我们的 SQL 中存在子查询，那么 id 的序号会递增，id 值越大优先级越高，越先被执行。当三个表依次嵌套，发现最里层的子查询 id 最大，最先执行。

mysql> EXPLAIN SELECT * FROM user u WHERE u.id = (SELECT ur.user_id FROM user_robot_relate ur WHERE ur.robot_id = (SELECT r.id FROM robot r WHERE r.name = '扫地机'));
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key          | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+
|  1 | PRIMARY     | u     | NULL       | const | PRIMARY       | PRIMARY      | 4       | const |    1 |   100.00 | NULL        |
|  2 | SUBQUERY    | ur    | NULL       | ref   | idx_robot_id  | idx_robot_id | 4       | const |    1 |   100.00 | Using where |
|  3 | SUBQUERY    | r     | NULL       | ALL   | NULL          | NULL         | NULL    | NULL  |    3 |    33.33 | Using where |
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+

3.1.3 以上两种同时存在

将上边的 SQL 稍微修改一下，增加一个子查询，发现 id 的以上两种同时存在。相同 id 划分为一组，这样就有三个组，同组的从上往下顺序执行，不同组 id 值越大，优先级越高，越先执行。

mysql> EXPLAIN SELECT * FROM user u WHERE u.id = (SELECT ur.user_id FROM user_robot_relate ur WHERE ur.robot_id = (SELECT r.id FROM robot r WHERE r.name = '扫地机')) AND u.id IN (SELECT u.id FROM user u WHERE u.name = 'riemann');
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key          | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+
|  1 | PRIMARY     | u     | NULL       | const | PRIMARY       | PRIMARY      | 4       | const |    1 |   100.00 | NULL        |
|  1 | PRIMARY     | u     | NULL       | const | PRIMARY       | PRIMARY      | 4       | const |    1 |   100.00 | NULL        |
|  2 | SUBQUERY    | ur    | NULL       | ref   | idx_robot_id  | idx_robot_id | 4       | const |    1 |   100.00 | Using where |
|  3 | SUBQUERY    | r     | NULL       | ALL   | NULL          | NULL         | NULL    | NULL  |    3 |    33.33 | Using where |
+----+-------------+-------+------------+-------+---------------+--------------+---------+-------+------+----------+-------------+

3.2 select_type

select_type：表示 select 查询的类型，主要是用于区分各种复杂的查询，例如：普通查询、联合查询、子查询等。

mysql> EXPLAIN SELECT t.user_id, (SELECT u.id FROM user u) o FROM (SELECT ur.user_id, ur.robot_id FROM user_robot_relate ur WHERE ur.id = 2) t UNION (SELECT r.id, r.name FROM robot r);
+----+--------------+------------+------------+-------+---------------+---------+---------+-------+------+----------+-----------------+
| id | select_type  | table      | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra           |
+----+--------------+------------+------------+-------+---------------+---------+---------+-------+------+----------+-----------------+
|  1 | PRIMARY      | ur         | NULL       | const | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | NULL            |
|  2 | SUBQUERY     | u          | NULL       | index | NULL          | PRIMARY | 4       | NULL  |    2 |   100.00 | Using index     |
|  4 | UNION        | r          | NULL       | ALL   | NULL          | NULL    | NULL    | NULL  |    3 |   100.00 | NULL            |
| NULL | UNION RESULT |  | NULL       | ALL   | NULL          | NULL    | NULL    | NULL  | NULL |     NULL | Using temporary |
+----+--------------+------------+------------+-------+---------------+---------+---------+-------+------+----------+-----------------+

3.3 table

查询的表名，并不一定是真实存在的表，有别名显示别名，也可能为临时表，例如上边的 DERIVED、等。

3.4 partitions

查询时匹配到的分区信息，对于非分区表值为 NULL，当查询的是分区表时，partitions 显示分区表命中的分区情况。

3.5 type

type：查询使用了何种类型，它在 SQL优化中是一个非常重要的指标，以下性能从好到坏依次是：

mysql> EXPLAIN SELECT * FROM robot WHERE id = 1;
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | robot | NULL       | const | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+

mysql> EXPLAIN SELECT u.name FROM user u, user_robot_relate ur WHERE u.id = ur.id; 
+----+-------------+-------+------------+--------+---------------+---------+---------+-----------+------+----------+-------------+
| id | select_type | table | partitions | type   | possible_keys | key     | key_len | ref       | rows | filtered | Extra       |
+----+-------------+-------+------------+--------+---------------+---------+---------+-----------+------+----------+-------------+
|  1 | SIMPLE      | u     | NULL       | ALL    | PRIMARY       | NULL    | NULL    | NULL      |    2 |   100.00 | NULL        |
|  1 | SIMPLE      | ur    | NULL       | eq_ref | PRIMARY       | PRIMARY | 4       | test.u.id |    1 |   100.00 | Using index |
+----+-------------+-------+------------+--------+---------------+---------+---------+-----------+------+----------+-------------+

mysql> EXPLAIN SELECT id FROM user_robot_relate WHERE user_id = 2; 
+----+-------------+-------------------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+
| id | select_type | table             | partitions | type | possible_keys | key         | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------------------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | user_robot_relate | NULL       | ref  | idx_user_id   | idx_user_id | 4       | const |    1 |   100.00 | Using index |
+----+-------------+-------------------+------------+------+---------------+-------------+---------+-------+------+----------+-------------+

-- 为了模拟这个场景，我又新增了一个 user_test 表。
mysql> CREATE TABLE `user_test` (
    -> `id` INT (11) NOT NULL AUTO_INCREMENT,
    -> `name` VARCHAR (20) DEFAULT NULL COMMENT "用户名",
    -> PRIMARY KEY (`id`), 
    -> KEY `idx_name` (`name`)
    -> ) ENGINE = INNODB DEFAULT CHARSET = utf8mb4 COMMENT = "用户测试表";
Query OK, 0 rows affected (0.01 sec)

mysql> EXPLAIN SELECT id FROM user_test WHERE name = 'riemann' OR name IS NULL; 
+----+-------------+-----------+------------+-------------+---------------+----------+---------+-------+------+----------+--------------------------+
| id | select_type | table     | partitions | type        | possible_keys | key      | key_len | ref   | rows | filtered | Extra                    |
+----+-------------+-----------+------------+-------------+---------------+----------+---------+-------+------+----------+--------------------------+
|  1 | SIMPLE      | user_test | NULL       | ref_or_null | idx_name      | idx_name | 83      | const |    2 |   100.00 | Using where; Using index |
+----+-------------+-----------+------------+-------------+---------------+----------+---------+-------+------+----------+--------------------------+

-- 下边示例中同时使用到主键 id 和字段 user_id 的索引。
mysql> EXPLAIN SELECT * FROM user_robot_relate WHERE id > 1 AND user_id = 2; 
+----+-------------+-------------------+------------+-------------+---------------------+---------------------+---------+------+------+----------+---------------------------------------------------+
| id | select_type | table             | partitions | type        | possible_keys       | key                 | key_len | ref  | rows | filtered | Extra                                             |
+----+-------------+-------------------+------------+-------------+---------------------+---------------------+---------+------+------+----------+---------------------------------------------------+
|  1 | SIMPLE      | user_robot_relate | NULL       | index_merge | PRIMARY,idx_user_id | idx_user_id,PRIMARY | 8,4     | NULL |    1 |   100.00 | Using intersect(idx_user_id,PRIMARY); Using where |
+----+-------------+-------------------+------------+-------------+---------------------+---------------------+---------+------+------+----------+---------------------------------------------------+

value IN (SELECT primary_key FROM single_table WHERE some_expr)

value IN (SELECT key_column FROM single_table WHERE some_expr)

-- user_robot_relate 表中 id 为唯一主键，name 普通字段未建索引。
mysql> EXPLAIN SELECT * FROM user_robot_relate WHERE id BETWEEN 2 AND 3;
+----+-------------+-------------------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table             | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------------------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user_robot_relate | NULL       | range | PRIMARY       | PRIMARY | 4       | NULL |    2 |   100.00 | Using where |
+----+-------------+-------------------+------------+-------+---------------+---------+---------+------+------+----------+-------------+

从结果中看到只有对设置了索引的字段，做范围检索 type 才是 range。

mysql> EXPLAIN SELECT * FROM user WHERE name BETWEEN 2 AND 3;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    2 |    50.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+

-- id 为主键，不带 where 条件全表查询，type 结果为 index。
mysql> EXPLAIN SELECT id FROM robot;
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | robot | NULL       | index | NULL          | PRIMARY | 4       | NULL |    3 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+

mysql> EXPLAIN SELECT * FROM robot;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | SIMPLE      | robot | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    3 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+

3.6 possible_keys

mysql> EXPLAIN SELECT id FROM user; 
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | index | NULL          | PRIMARY | 4       | NULL |    2 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+

注意：想要使用到覆盖索引，我们在 select 时只取出需要的字段，不可 SELECT *，而且该字段建了索引。

mysql> EXPLAIN SELECT * FROM user;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    2 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+

3.12.2 Using where

Using where：查询时未找到可用的索引，进而通过 where 条件过滤获取所需数据，但要注意的是并不是所有带 where 语句的查询都会显示 Using where。

下边示例 name 并未用到索引，type 为 ALL，即 MySQL 通过全表扫描后再按 where 条件筛选数据。

mysql> EXPLAIN SELECT name FROM user WHERE name = 'riemann';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    2 |    50.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+

3.12.3 Using temporary

Using temporary：表示查询后结果需要使用临时表来存储，一般在排序或者分组查询时用到。

mysql> EXPLAIN SELECT name FROM user WHERE id IN (1, 2) GROUP BY name;
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra                                        |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------------------+
|  1 | SIMPLE      | user  | NULL       | range | PRIMARY       | PRIMARY | 4       | NULL |    2 |   100.00 | Using where; Using temporary; Using filesort |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------------------+

3.12.4 Using filesort

Using filesort：表示无法利用索引完成的排序操作，也就是 ORDER BY 的字段没有索引，通常这样的 SQL 都是需要优化的。

mysql> EXPLAIN SELECT id FROM user ORDER BY name;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra          |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    2 |   100.00 | Using filesort |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+

如果 ORDER BY 字段有索引就会用到覆盖索引，相比执行速度快很多。

mysql> EXPLAIN SELECT id FROM user ORDER BY id;
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | index | NULL          | PRIMARY | 4       | NULL |    2 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+

3.12.5 Using join buffer

Using join buffer：在我们联表查询的时候，如果表的连接条件没有用到索引，需要有一个连接缓冲区来存储中间结果。

mysql> EXPLAIN SELECT u.name FROM user u, user_test t WHERE u.name = t.name;
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+----------------------------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                                              |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+----------------------------------------------------+
|  1 | SIMPLE      | t     | NULL       | index | idx_name      | idx_name | 83      | NULL |    1 |   100.00 | Using index                                        |
|  1 | SIMPLE      | u     | NULL       | ALL   | NULL          | NULL     | NULL    | NULL |    2 |    50.00 | Using where; Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+----------------------------------------------------+

3.12.6 Impossible where

Impossible where：表示在我们用不太正确的 where 语句，导致没有符合条件的行。

mysql> EXPLAIN SELECT name FROM user WHERE 1=2;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra            |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+
|  1 | SIMPLE      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | Impossible WHERE |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+

3.12.7 No tables used

No tables used：我们的查询语句中没有 FROM 子句，或者有 FROM DUAL 子句。

mysql> EXPLAIN SELECT now();
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra          |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+
|  1 | SIMPLE      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | No tables used |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+

今天带大家了解了MySQL的相关知识，希望对你有所帮助；关于数据库的技术知识我们会一点点深入介绍，欢迎大家关注golang学习网公众号，一起学习编程~

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