假如表中包含一列为auto_increment,
如果是Myisam类型的引擎,那么在删除了最新一笔数据,无论是否重启Mysql,下一次插入之后仍然会使用上次删除的最大ID+1.
mysql> create table test_myisam (id int not null auto_increment primary key, name char(5)) engine=myisam; Query OK, 0 rows affected (0.04 sec) mysql> insert into test_myisam (name) select ‘a‘; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into test_myisam (name) select ‘b‘; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into test_myisam (name) select ‘c‘; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into test_myisam (name) select name from test_myisam; Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from test_myisam; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | b | | 3 | c | | 4 | a | | 5 | b | | 6 | c | +----+------+ 6 rows in set (0.00 sec) mysql> delete from test_myisam where id=6; Query OK, 1 row affected (0.00 sec)
mysql> insert into test_myisam(name) select ‘d‘; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> select * from test_myisam; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | b | | 3 | c | | 4 | a | | 5 | b | | 7 | d | +----+------+ 6 rows in set (0.00 sec)
下面是对Innodb表的测试。
mysql> create table test_innodb(id int not null auto_increment primary key, name char(5)) engine=innodb; Query OK, 0 rows affected (0.26 sec) mysql> insert into test_innodb (name)select ‘a‘; Query OK, 1 row affected (0.06 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into test_innodb (name)select ‘b‘; Query OK, 1 row affected (0.06 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> insert into test_innodb (name)select ‘c‘; Query OK, 1 row affected (0.07 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> select * from test_innodb; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | b | | 3 | c | +----+------+ 3 rows in set (0.00 sec) mysql> delete from test_innodb where id=3; Query OK, 1 row affected (0.05 sec) mysql> insert into test_innodb (name)select ‘d‘; Query OK, 1 row affected (0.20 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> select * from test_innodb; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | b | | 4 | d | +----+------+ 3 rows in set (0.00 sec) mysql> exit Bye [2@a data]$ mysql -uroot -pwsdad Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 5 Server version: 5.5.37-log Source distribution Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement. mysql> use wison Database changed mysql> delete from test_innodb where id=4; Query OK, 1 row affected (0.07 sec) mysql> exit Bye [2@a data]$ sudo service mysql restart Shutting down MySQL... SUCCESS! Starting MySQL.. SUCCESS! [2@a data]$ mysql -uroot -pwison Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 1 Server version: 5.5.37-log Source distribution Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement. mysql> use wison Database changed mysql> insert into test_innodb (name) select ‘z‘; Query OK, 1 row affected (0.07 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> select * from test_innodb; +----+------+ | id | name | +----+------+ | 1 | a | | 2 | b | | 3 | z | +----+------+ 3 rows in set (0.00 sec)
可以看到在mysql数据库没有重启时,innodb的表新插入数据会是之前被删除的数据再加1.
但是当Mysql服务被重启后,再向InnodB的自增表表里插入数据,那么会使用当前Innodb表里的最大的自增列再加1.
原因:
Myisam类型存储引擎的表将最大的ID值是记录到数据文件中,不管是否重启最大的ID值都不会丢失。但是InnoDB表的最大的ID值是存在内存中的,若不重启Mysql服务,新加入数据会使用内存中最大的数据+1.但是重启之后,会使用当前表中最大的值再+1
感谢阅读此文,希望能帮助到大家,谢谢大家对本站的支持!
广告合作:本站广告合作请联系QQ:858582 申请时备注:广告合作(否则不回)
免责声明:本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除!
免责声明:本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除!
暂无评论...
RTX 5090要首发 性能要翻倍!三星展示GDDR7显存
三星在GTC上展示了专为下一代游戏GPU设计的GDDR7内存。
首次推出的GDDR7内存模块密度为16GB,每个模块容量为2GB。其速度预设为32 Gbps(PAM3),但也可以降至28 Gbps,以提高产量和初始阶段的整体性能和成本效益。
据三星表示,GDDR7内存的能效将提高20%,同时工作电压仅为1.1V,低于标准的1.2V。通过采用更新的封装材料和优化的电路设计,使得在高速运行时的发热量降低,GDDR7的热阻比GDDR6降低了70%。
更新日志
2024年11月23日
2024年11月23日
- 凤飞飞《我们的主题曲》飞跃制作[正版原抓WAV+CUE]
- 刘嘉亮《亮情歌2》[WAV+CUE][1G]
- 红馆40·谭咏麟《歌者恋歌浓情30年演唱会》3CD[低速原抓WAV+CUE][1.8G]
- 刘纬武《睡眠宝宝竖琴童谣 吉卜力工作室 白噪音安抚》[320K/MP3][193.25MB]
- 【轻音乐】曼托凡尼乐团《精选辑》2CD.1998[FLAC+CUE整轨]
- 邝美云《心中有爱》1989年香港DMIJP版1MTO东芝首版[WAV+CUE]
- 群星《情叹-发烧女声DSD》天籁女声发烧碟[WAV+CUE]
- 刘纬武《睡眠宝宝竖琴童谣 吉卜力工作室 白噪音安抚》[FLAC/分轨][748.03MB]
- 理想混蛋《Origin Sessions》[320K/MP3][37.47MB]
- 公馆青少年《我其实一点都不酷》[320K/MP3][78.78MB]
- 群星《情叹-发烧男声DSD》最值得珍藏的完美男声[WAV+CUE]
- 群星《国韵飘香·贵妃醉酒HQCD黑胶王》2CD[WAV]
- 卫兰《DAUGHTER》【低速原抓WAV+CUE】
- 公馆青少年《我其实一点都不酷》[FLAC/分轨][398.22MB]
- ZWEI《迟暮的花 (Explicit)》[320K/MP3][57.16MB]