MySQL8.0新特性-易微帮

1、新增降序索引

MySQL 5.7：在语法上支持降序索引，但实际上创建的仍然是升序索引

MySQL 8.0：真正支持降序索引（只有Innodb存储引擎支持降序索引）

# ====MySQL 5.7演示====
mysql> create table t1(c1 int,c2 int,index idx_c1_c2(c1,c2 desc));
Query OK, 0 rows affected (0.04 sec)

mysql> insert into t1 (c1,c2) values(1, 10),(2,50),(3,50),(4,100),(5,80);
Query OK, 5 rows affected (0.02 sec)

mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  KEY `idx_c1_c2` (`c1`,`c2`)    --注意这里，c2字段是升序
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> explain select * from t1 order by c1,c2 desc;  --5.7也会使用索引，但是Extra字段里有filesort文件排序
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra                       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    1 |   100.00 | Using index; Using filesort |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
1 row in set, 1 warning (0.01 sec)

# ====MySQL 8.0演示====
mysql> create table t1(c1 int,c2 int,index idx_c1_c2(c1,c2 desc));
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t1 (c1,c2) values(1, 10),(2,50),(3,50),(4,100),(5,80);
Query OK, 5 rows affected (0.02 sec)

mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `c1` int DEFAULT NULL,
  `c2` int DEFAULT NULL,
  KEY `idx_c1_c2` (`c1`,`c2` DESC)  --降序索引是生效的
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> explain select * from t1 order by c1,c2 desc;  --Extra字段里没有filesort文件排序，充分利用了降序索引
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    1 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from t1 order by c1 desc,c2;  --Extra字段里有Backward index scan，意思是反向扫描索引;
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+----------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra                            |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+----------------------------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    1 |   100.00 | Backward index scan; Using index |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+----------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from t1 order by c1 desc,c2 desc;  --Extra字段里有filesort文件排序，排序必须按照每个字段定义的排序或按相反顺序才能充分利用索引
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
| id | select_type | table | partitions | type  | possible_keys | key       | key_len | ref  | rows | filtered | Extra                       |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
|  1 | SIMPLE      | t1    | NULL       | index | NULL          | idx_c1_c2 | 10      | NULL |    1 |   100.00 | Using index; Using filesort |
+----+-------------+-------+------------+-------+---------------+-----------+---------+------+------+----------+-----------------------------+
1 row in set, 1 warning (0.00 sec)

2、group by 不再隐式排序

MySQL 5.7：对于 group by 字段会排序

MySQL 8.0：对于 group by 字段不再隐式排序，如需要排序，必须显式加上order by 子句

# ====MySQL 5.7演示====
mysql> select count(*),c2 from t1 group by c2;
+----------+------+
| count(*) | c2   |
+----------+------+
|        1 |   10 |
|        2 |   50 |
|        1 |   80 |
|        1 |  100 |
+----------+------+
4 rows in set (0.00 sec)

# ====MySQL 8.0演示====
mysql> select count(*),c2 from t1 group by c2;   --8.0版本group by不再默认排序
+----------+------+
| count(*) | c2   |
+----------+------+
|        1 |   10 |
|        2 |   50 |
|        1 |  100 |
|        1 |   80 |
+----------+------+
4 rows in set (0.00 sec)

mysql> select count(*),c2 from t1 group by c2 order by c2;  --8.0版本group by不再默认排序，需要自己加order by
+----------+------+
| count(*) | c2   |
+----------+------+
|        1 |   10 |
|        2 |   50 |
|        1 |   80 |
|        1 |  100 |
+----------+------+
4 rows in set (0.00 sec)

3、增加隐藏索引

MySQL 8.0：

使用 invisible 关键字在创建表或者进行表变更中设置索引为隐藏索引（注意：主键不能设置为 invisible）
隐藏索引只是对于业务是不可见的，Mysql后台还是会维护这个索引。因为在查询时优化器不会使用该索引，即使使用force index，优化器也不会使用该索引，同时也不会报索引不存在的错误，因为索引仍然真实存在
需要时，可以把隐藏索引快速恢复成可见
软删除就可以使用隐藏索引，比如我们觉得某个索引没用了，但是担心删除后这个索引在某些时候还是有用的。于是又得把这个索引加回来，那如果表数据量很大的话，这种操作是很耗时的，成本较高。这时，我们可以将索引先设置为隐藏索引，等到真的确认索引没用了再删除。

# 创建t2表，里面的c2字段为隐藏索引
mysql> create table t2(c1 int, c2 int, index idx_c1(c1), index idx_c2(c2) invisible);
Query OK, 0 rows affected (0.02 sec)

mysql> show index from t2\G
*************************** 1. row ***************************
        Table: t2
   Non_unique: 1
     Key_name: idx_c1
 Seq_in_index: 1
  Column_name: c1
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
      Visible: YES --idx_c1索引可见
   Expression: NULL
*************************** 2. row ***************************
        Table: t2
   Non_unique: 1
     Key_name: idx_c2
 Seq_in_index: 1
  Column_name: c2
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
      Visible: NO   --idx_c2索引被隐藏
   Expression: NULL
2 rows in set (0.00 sec)

mysql> explain select * from t2 where c1=1;
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | t2    | NULL       | ref  | idx_c1        | idx_c1 | 5       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from t2 where c2=1;  --idx_c2索引不会被使用
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t2    | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    1 |   100.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

# 如果想测试隐藏索引，可以在会话级别下，打开开关，在查询时优化器可以使用Mysql的隐藏索引
mysql> select @@optimizer_switch\G   --查看各种参数
*************************** 1. row ***************************
@@optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on,use_invisible_indexes=off,skip_scan=on,hash_join=on
1 row in set (0.00 sec)

mysql> set session optimizer_switch="use_invisible_indexes=on";  ----在会话级别设置查询优化器可以看到隐藏索引
Query OK, 0 rows affected (0.00 sec)

mysql> select @@optimizer_switch\G
*************************** 1. row ***************************
@@optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on,use_invisible_indexes=on,skip_scan=on,hash_join=on
1 row in set (0.00 sec)

mysql> explain select * from t2 where c2=1;
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | t2    | NULL       | ref  | idx_c2        | idx_c2 | 5       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

# 测试完毕，觉得隐藏索引可以使用，再修改成可见的
mysql> alter table t2 alter index idx_c2 visible;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

4、新增函数索引

MySQL 5.7：函数作用在索引字段上，会使索引失效

MySQL 8.0：引入函数索引，支持在索引中使用函数。函数索引基于虚拟列功能实现，在MySQL中相当于新增了一个列，这个列会根据你的函数来进行计算结果，然后使用函数索引的时候就会用这个计算后的列作为索引

mysql> create table t3(c1 varchar(10),c2 varchar(10));
Query OK, 0 rows affected (0.02 sec)

mysql> create index idx_c1 on t3(c1);     --创建普通索引
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> create index func_idx on t3((UPPER(c2)));  --创建一个大写的函数索引
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from t3\G
*************************** 1. row ***************************
        Table: t3
   Non_unique: 1
     Key_name: idx_c1
 Seq_in_index: 1
  Column_name: c1
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
      Visible: YES
   Expression: NULL
*************************** 2. row ***************************
        Table: t3
   Non_unique: 1
     Key_name: func_idx
 Seq_in_index: 1
  Column_name: NULL
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: 
Index_comment: 
      Visible: YES
   Expression: upper(`c2`)    --函数表达式
2 rows in set (0.00 sec)

mysql> explain select * from t3 where upper(c1)='ZHUGE'; -- 普通索引没有使用到
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | t3    | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    1 |   100.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from t3 where upper(c2)='ZHUGE';  --使用了函数索引
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | t3    | NULL       | ref  | func_idx      | func_idx | 43      | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

5、innodb存储引擎select for update跳过锁等待

MySQL 5.7：select…for update，如果获取不到锁，会一直等待，直到innodb_lock_wait_timeout超时

MySQL 8.0：select … for share（8.0新增加查询共享锁的语法）或 select … for update，可以跳过锁等待，或者跳过锁定

1. 通过添加 nowait 语法，查询会报错立即返回，不等待锁，提高系统性能
2. 通过添加 skip locked 语法，也会立即返回，区别是不会报错，并且返回不包含被锁定的行的结果集，提高系统性能（比如购票场景，返回没有被锁定的座位）

# session1:
mysql> select * from t1;
+------+------+
| c1   | c2   |
+------+------+
|    1 |   10 |
|    2 |   50 |
|    3 |   50 |
|    4 |  100 |
|    5 |   80 |
+------+------+
5 rows in set (0.00 sec)
    
mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> update t1 set c2 = 60 where c1 = 2;     --锁定第二条记录
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0


# session2:    
mysql> select * from t1 where c1 = 2 for update;   --等待超时
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

mysql> select * from t1 where c1 = 2 for update nowait;   --查询立即返回
ERROR 3572 (HY000): Statement aborted because lock(s) could not be acquired immediately and NOWAIT is set.

mysql> select * from t1 for update skip locked;  --查询立即返回，过滤掉了第二行记录
+------+------+
| c1   | c2   |
+------+------+
|    1 |   10 |
|    3 |   50 |
|    4 |  100 |
|    5 |   80 |
+------+------+
4 rows in set (0.00 sec)

6、新增innodb_dedicated_server自适应参数

MySQL 8.0：InnoDB会根据服务器上检测到的内存大小自动调整 innodb_buffer_pool_size，innodb_log_file_size 等参数，尽可能的冲分利用系统资源

默认是关闭的，不建议开启该参数，因为如果服务器不是专用来给MySQL数据库的，不然会影响其它程序

mysql> show variables like '%innodb_dedicated_server%';   --默认是OFF关闭，修改为ON打开
+-------------------------+-------+
| Variable_name           | Value |
+-------------------------+-------+
| innodb_dedicated_server | OFF   |
+-------------------------+-------+
1 row in set (0.02 sec)

7、死锁检查控制

MySQL 8.0：增加动态变量 innodb_deadlock_detect，用于控制系统是否执行 InnoDB 死锁检查，默认是打开的。

死锁检测会耗费数据库性能的，对于高并发的系统，可以关闭该功能，提高系统性能。前提是要确保系统极少情况会发生死锁，同时要将锁等待超时参数调小一点，以防出现死锁等待过久的情况

mysql> show variables like '%innodb_deadlock_detect%';  --默认是打开的
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| innodb_deadlock_detect | ON    |
+------------------------+-------+
1 row in set, 1 warning (0.01 sec)

8、undo文件不再使用系统表空间

MySQL 5.7：默认创建ib开头的系统表空间

MySQL 8.0：默认创建2个UNDO表空间，不再使用系统表空间
在这里插入图片描述

9、 binlog日志过期时间精确到秒

MySQL 5.7：设置expire_logs_days参数，只能精确到天

MySQL 8.0：参数名称发生变化，设置binlog_expire_logs_seconds参数，并且可以精确到秒

10、窗口函数(Window Functions)：也称分析函数

MySQL 8.0：

新增窗口函数的概念，在聚合函数（ SUM、COUNT ）后面加上over()就变成窗口函数，在over括号里可以加上partition by等分组关键字指定如何分组
窗口函数即便分组也不会将多行查询结果合并为一行，而是将结果放回多行当中

# 创建一张账户余额表
CREATE TABLE `account_channel` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL COMMENT '姓名',
  `channel` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL COMMENT '账户渠道',
  `balance` int DEFAULT NULL COMMENT '余额',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB

# 插入一些示例数据
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('1', 'zhuge', 'wx', '100');
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('2', 'zhuge', 'alipay', '200');
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('3', 'zhuge', 'yinhang', '300');
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('4', 'lilei', 'wx', '200');
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('5', 'lilei', 'alipay', '100');
INSERT INTO `test`.`account_channel` (`id`, `name`, `channel`, `balance`) VALUES ('6', 'hanmeimei', 'wx', '500');

mysql> select * from account_channel;
+----+-----------+---------+---------+
| id | name      | channel | balance |
+----+-----------+---------+---------+
|  1 | zhuge     | wx      |     100 |
|  2 | zhuge     | alipay  |     200 |
|  3 | zhuge     | yinhang |     300 |
|  4 | lilei     | wx      |     200 |
|  5 | lilei     | alipay  |     100 |
|  6 | hanmeimei | wx      |     500 |
+----+-----------+---------+---------+
6 rows in set (0.00 sec)

mysql> select name,sum(balance) from account_channel group by name;
+-----------+--------------+
| name      | sum(balance) |
+-----------+--------------+
| zhuge     |          600 |
| lilei     |          300 |
| hanmeimei |          500 |
+-----------+--------------+
3 rows in set (0.00 sec)

# sum(balance) over(partition by name) 窗口函数
mysql> select name,channel,balance,sum(balance) over(partition by name) as sum_balance from account_channel;
+-----------+---------+---------+-------------+
| name      | channel | balance | sum_balance |
+-----------+---------+---------+-------------+
| hanmeimei | wx      |     500 |         500 |
| lilei     | wx      |     200 |         300 |
| lilei     | alipay  |     100 |         300 |
| zhuge     | wx      |     100 |         600 |
| zhuge     | alipay  |     200 |         600 |
| zhuge     | yinhang |     300 |         600 |
+-----------+---------+---------+-------------+
6 rows in set (0.00 sec)

mysql> select name,channel,balance,sum(balance) over(partition by name order by balance) as sum_balance from account_channel;
+-----------+---------+---------+-------------+
| name      | channel | balance | sum_balance |
+-----------+---------+---------+-------------+
| hanmeimei | wx      |     500 |         500 |
| lilei     | alipay  |     100 |         100 |
| lilei     | wx      |     200 |         300 |
| zhuge     | wx      |     100 |         100 |
| zhuge     | alipay  |     200 |         300 |
| zhuge     | yinhang |     300 |         600 |
+-----------+---------+---------+-------------+
6 rows in set (0.00 sec)


# over()里如果不加条件，则会使用Where条件所有行
mysql> select name,channel,balance,sum(balance) over() as sum_balance from account_channel;
+-----------+---------+---------+-------------+
| name      | channel | balance | sum_balance |
+-----------+---------+---------+-------------+
| zhuge     | wx      |     100 |        1400 |
| zhuge     | alipay  |     200 |        1400 |
| zhuge     | yinhang |     300 |        1400 |
| lilei     | wx      |     200 |        1400 |
| lilei     | alipay  |     100 |        1400 |
| hanmeimei | wx      |     500 |        1400 |
+-----------+---------+---------+-------------+
6 rows in set (0.00 sec)

mysql> select name,channel,balance,avg(balance) over(partition by name) as avg_balance from account_channel;
+-----------+---------+---------+-------------+
| name      | channel | balance | avg_balance |
+-----------+---------+---------+-------------+
| hanmeimei | wx      |     500 |    500.0000 |
| lilei     | wx      |     200 |    150.0000 |
| lilei     | alipay  |     100 |    150.0000 |
| zhuge     | wx      |     100 |    200.0000 |
| zhuge     | alipay  |     200 |    200.0000 |
| zhuge     | yinhang |     300 |    200.0000 |
+-----------+---------+---------+-------------+
6 rows in set (0.00 sec)

专用窗口函数：

序号函数：ROW_NUMBER()、RANK()、DENSE_RANK()
分布函数：PERCENT_RANK()、CUME_DIST()
前后函数：LAG()、LEAD()
头尾函数：FIRST_VALUE()、LAST_VALUE()
其它函数：NTH_VALUE()、NTILE()

# 按照balance字段排序，展示序号
mysql> select name,channel,balance,row_number() over(order by balance) as row_number1 from account_channel;
+-----------+---------+---------+-------------+
| name      | channel | balance | row_number1 |
+-----------+---------+---------+-------------+
| zhuge     | wx      |     100 |           1 |
| lilei     | alipay  |     100 |           2 |
| zhuge     | alipay  |     200 |           3 |
| lilei     | wx      |     200 |           4 |
| zhuge     | yinhang |     300 |           5 |
| hanmeimei | wx      |     500 |           6 |
+-----------+---------+---------+-------------+
6 rows in set (0.00 sec)

# 按照balance字段排序，first_value()选出排第一的余额
mysql> select name,channel,balance,first_value(balance) over(order by balance) as first1 from account_channel;
+-----------+---------+---------+--------+
| name      | channel | balance | first1 |
+-----------+---------+---------+--------+
| zhuge     | wx      |     100 |    100 |
| lilei     | alipay  |     100 |    100 |
| zhuge     | alipay  |     200 |    100 |
| lilei     | wx      |     200 |    100 |
| zhuge     | yinhang |     300 |    100 |
| hanmeimei | wx      |     500 |    100 |
+-----------+---------+---------+--------+
6 rows in set (0.01 sec)

11、默认字符集由latin1变为utf8mb4

MySQL 5.7：默认字符集为latin1，utf8指向的是utf8mb3

MySQL 8.0：默认字符集为utf8mb4，utf8默认指向的也是utf8mb4

12、MyISAM系统表全部换成InnoDB表

MySQL 8.0：系统表和数据字典表全部改为InnoDB存储引擎

13、元数据存储变动

MySQL 8.0：删除之前版本的元数据文件，例如表结构.frm等文件，全部集中放入mysql.ibd文件里。如图所示，test库文件夹里已经没有了frm文件
在这里插入图片描述

14、自增变量持久化

MySQL 5.7：在MySQL重启后，会重置AUTO_INCREMENT=max(primary key)+1，在某些业务场景下会报主键冲突的错误或其它难以发现的问题

MySQL 8.0：对AUTO_INCREMENT值进行持久化，MySQL重启后，该值将不会改变

# ====MySQL 5.7演示====
mysql> create table t(id int auto_increment primary key,c1 varchar(20));
Query OK, 0 rows affected (0.03 sec)

mysql> insert into t(c1) values('zhuge1'),('zhuge2'),('zhuge3');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
|  3 | zhuge3 |
+----+--------+
3 rows in set (0.00 sec)

mysql> delete from t where id = 3;
Query OK, 1 row affected (0.01 sec)

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
+----+--------+
2 rows in set (0.00 sec)

mysql> exit;
Bye

# 如果不重启Mysql服务，插入一条数据它的主键Id就是4

# 但是重启MySQL服务，并重新连接MySQL。它会重置自增ID,从3开始
mysql> insert into t(c1) values('zhuge4');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
|  3 | zhuge4 |
+----+--------+
3 rows in set (0.00 sec)

# ====MySQL 8.0演示====
mysql> create table t(id int auto_increment primary key,c1 varchar(20));
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t(c1) values('zhuge1'),('zhuge2'),('zhuge3');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
|  3 | zhuge3 |
+----+--------+
3 rows in set (0.00 sec)

mysql> delete from t where id = 3;
Query OK, 1 row affected (0.01 sec)

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
+----+--------+
2 rows in set (0.00 sec)

mysql> exit;
Bye
[root@localhost ~]# service mysqld restart
Shutting down MySQL.... SUCCESS! 
Starting MySQL... SUCCESS! 

# 重新连接MySQL
mysql> insert into t(c1) values('zhuge4');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t;  --生成的id为4，不是3
+----+--------+
| id | c1     |
+----+--------+
|  1 | zhuge1 |
|  2 | zhuge2 |
|  4 | zhuge4 |
+----+--------+
3 rows in set (0.00 sec)

mysql> update t set id = 5 where c1 = 'zhuge1';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  2 | zhuge2 |
|  4 | zhuge4 |
|  5 | zhuge1 |
+----+--------+
3 rows in set (0.00 sec)

mysql> insert into t(c1) values('zhuge5');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t;
+----+--------+
| id | c1     |
+----+--------+
|  2 | zhuge2 |
|  4 | zhuge4 |
|  5 | zhuge1 |
|  6 | zhuge5 |
+----+--------+
4 rows in set (0.00 sec)

15、DDL原子化

InnoDB表的DDL支持事务完整性，要么成功要么回滚。

MySQL 8.0 开始支持原子 DDL 操作，其中与表相关的原子 DDL 只支持 InnoDB 存储引擎。一个原子 DDL 操作内容包括：更新数据字典，存储引擎层的操作，在 binlog 中记录 DDL 操作。支持与表相关的 DDL：数据库、表空间、表、索引的 CREATE、ALTER、DROP 以及 TRUNCATE TABLE。支持的其它 DDL ：存储程序、触发器、视图、UDF 的 CREATE、DROP 以及ALTER 语句。支持账户管理相关的 DDL：用户和角色的 CREATE、ALTER、DROP 以及适用的 RENAME等等。

# MySQL 5.7
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| account        |
| actor          |
| employee       |
| film           |
| film_actor     |
| leaf_id        |
| t1             |
| test_innodb    |
| test_myisam    |
| test_order_id  |
+----------------+
10 rows in set (0.01 sec)

mysql> drop table t1,t2;  //删除表报错不会回滚，t1表会被删除
ERROR 1051 (42S02): Unknown table 'test.t2'
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| account        |
| actor          |
| employee       |
| film           |
| film_actor     |
| leaf_id        |
| test_innodb    |
| test_myisam    |
| test_order_id  |
+----------------+
9 rows in set (0.00 sec)

# MySQL 8.0  
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| account        |
| actor          |
| employee       |
| film           |
| film_actor     |
| leaf_id        |
| t1             |
| test_innodb    |
| test_myisam    |
| test_order_id  |
+----------------+
10 rows in set (0.00 sec)

mysql> drop table t1,t2;  //删除表报错会回滚，t1表依然还在
ERROR 1051 (42S02): Unknown table 'test.t2'
mysql> show tables;  
+----------------+
| Tables_in_test |
+----------------+
| account        |
| actor          |
| employee       |
| film           |
| film_actor     |
| leaf_id        |
| t1             |
| test_innodb    |
| test_myisam    |
| test_order_id  |
+----------------+
10 rows in set (0.00 sec)

16、参数修改持久化

MySQL 5.7：set global 设置的变量参数在mysql重启后会失效
MySQL 8.0：支持在线修改全局参数并持久化，通过加上PERSIST关键字，可以将修改的参数持久化到新的配置文件（mysqld-auto.cnf）中。重启MySQL时，会从该配置文件获取到最新的配置参数

mysql> set persist innodb_lock_wait_timeout=25;
系统会在数据目录下生成一个包含json格式的mysqld-auto.cnf 的文件，格式化后如下所示，当my.cnf 和mysqld-auto.cnf 同时存在时，后者具有更高优先级。
{
    "Version": 1,
    "mysql_server": {
        "innodb_lock_wait_timeout": {
            "Value": "25",
            "Metadata": {
                "Timestamp": 1675290252103863,
                "User": "root",
                "Host": "localhost"
            }
        }
    }
}```

MySQL8.0新特性