MySQL "Show table status"，自动增量不正确

Question

我在Mysql中创建了一个新表，添加了一些行，但显示表的Auto_increment字段仍然返回NULL。

mysql手册说:这个字段应该返回:“下一个Auto_increment值”

https://dev.mysql.com/doc/refman/8.0/en/show-table-status.html

我做错了什么？

如何正确找到下一个 auto_increment 值？

<小时/>

重现步骤:

create table `test` (
  `id` int(5) not null auto_increment,
  `name` varchar(256),
  PRIMARY KEY(`id`)
);

然后我运行:

show table status where name like 'test';

结果:

Name,   Engine,   Version, ...,  Auto_increment, ... 
'test', 'InnoDB', '10',    ...,  NULL, ...

然后我运行:

insert into test values(null,'name1');
insert into test values(null,'name2');
insert into test values(null,'name3');

编辑:-其他插入语法-

insert into test (name) values('name4');
insert into test (name) values('name5');
insert into test (name) values('name6');

获取表的状态

show table status where name like 'test';

结果

Name,   Engine,   Version, ...,  Auto_increment, ... 
'test', 'InnoDB', '10',    ...,  NULL, ...

表格中的数据

select * from test;

结果:

1   name1
2   name2
3   name3

供您引用:

SHOW VARIABLES LIKE "%version%";

结果:

'innodb_version', '8.0.12'
'protocol_version', '10'
'slave_type_conversions', ''
'tls_version', 'TLSv1,TLSv1.1,TLSv1.2'
'version', '8.0.12'
'version_comment', 'MySQL Community Server - GPL'
'version_compile_machine', 'x86_64'
'version_compile_os', 'Win64'
'version_compile_zlib', '1.2.11'

编辑:自动提交:

SHOW VARIABLES LIKE "autocommit";

结果:

'autocommit', 'ON'

编辑:

过了一会儿，它会自动开始工作。没有明确的原因如何让它开始工作。

Answer 1

这是一个功能..而不是一个错误。

表统计信息已缓存。要禁用缓存并始终拥有最新版本，您应该将指示缓存清除持续时间的服务器变量更改为 0:

SET PERSIST information_schema_stats_expiry = 0

该属性的默认值在Mysql 8.x中已更改为86400(24小时)

示例:

SET PERSIST information_schema_stats_expiry = 86400
-- 86400 is the default value of mysql 8.x  if you have never changed this you don't need to set this


show variables like 'information_schema_stats_expiry';

+---------------------------------+-------+
| Variable_name                   | Value |
+---------------------------------+-------+
| information_schema_stats_expiry | 86400 |
+---------------------------------+-------+

create schema mytest;

create table `test` (
    `id` int(5) not null auto_increment,
    `name` varchar(256),
    PRIMARY KEY(`id`)
);

insert into test values(null,'name1')
insert into test values(null,'name2')
insert into test values(null,'name3')

show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time         | Update_time         | Check_time | Collation          | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB |      10 | Dynamic    |    3 |           5461 |       16384 |               0 |            0 |         0 |              4 | 2018-10-09 15:32:15 | 2018-10-09 15:32:16 | NULL       | utf8mb4_0900_ai_ci |     NULL |                |         |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The Auto_increment field is correctly set to 4.. but is now cached.

insert into test values(null,'name3');

show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time         | Update_time         | Check_time | Collation          | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB |      10 | Dynamic    |    3 |           5461 |       16384 |               0 |            0 |         0 |              4 | 2018-10-09 15:32:15 | 2018-10-09 15:32:16 | NULL       | utf8mb4_0900_ai_ci |     NULL |                |         |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The Auto_increment is still 4 (it was cached).

drop schema mytest

现在我们更改配置:

SET PERSIST information_schema_stats_expiry = 0

我们运行相同的测试:

show variables like 'information_schema_stats_expiry'


+---------------------------------+-------+
| Variable_name                   | Value |
+---------------------------------+-------+
| information_schema_stats_expiry | 0     |
+---------------------------------+-------+

create schema mytest;
create table `test` (
    `id` int(5) not null auto_increment,
    `name` varchar(256),
    PRIMARY KEY(`id`)
);

insert into test values(null,'name1');
insert into test values(null,'name2');
insert into test values(null,'name3');

show table status where name like 'test';

+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time         | Update_time         | Check_time | Collation          | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB |      10 | Dynamic    |    3 |           5461 |       16384 |               0 |            0 |         0 |              4 | 2018-10-09 15:32:49 | 2018-10-09 15:32:49 | NULL       | utf8mb4_0900_ai_ci |     NULL |                |         |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
--  Auto_increment is 4, but the result is not cached!

insert into test values(null,'name3');



show table status where name like 'test';


+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time         | Update_time         | Check_time | Collation          | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB |      10 | Dynamic    |    4 |           4096 |       16384 |               0 |            0 |         0 |              5 | 2018-10-09 15:32:49 | 2018-10-09 15:32:49 | NULL       | utf8mb4_0900_ai_ci |     NULL |                |         |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The  Auto_increment field is now 5 (a correct, not cached value)

drop schema mytest;