《MYSQL數據庫解析mysql中的auto_increment的問題》要點:
本文介紹了MYSQL數據庫解析mysql中的auto_increment的問題,希望對您有用。如果有疑問,可以聯系我們。
MYSQL入門今兒在逛論壇時,發現一個看似很簡單的問題,卻引起了大家的廣泛關注:
這是一道很早的面試題:
一張表,里面有ID自增主鍵,當insert了17條記錄之后,刪除了第15,16,17條記錄,再把Mysql重啟,再insert一條記錄,這條記錄的ID是18還是15 .
答案:
MYSQL入門如果表的類型是MyISAM,那么是18.
因為MyISAM表會把自增主鍵的最大ID記錄到數據文件里,重啟MySQL自增主鍵的最大ID也不會丟失.
如果表的類型是InnoDB,那么是15.
InnoDB表只是把自增主鍵的最大ID記錄到內存中,所以重啟數據庫或者是對表進行OPTIMIZE操作,都會導致最大ID丟失.
MYSQL入門自己也做了個實驗,結果證實了上面的說法.真是慚愧啊,看似簡單的問題自己也打錯了.
MYSQL入門mysql> delete from test1 where id in (10,11,9);
Query OK, 3 rows affected (0.03 sec)
MYSQL入門mysql> show create table test1;
?CREATE TABLE `test1` (
? `id` int(11) NOT NULL auto_increment,
? `name` varchar(10) default NULL,
? PRIMARY KEY? (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=<SPAN style="COLOR: #ff0000">12</SPAN> DEFAULT CHARSET=utf8 |
mysql> exit;
Bye
[root@fsailing1 ~]# service mysqld restart
停止 MySQL:?????????????????????????????????????????????? [確定]
啟動 MySQL:?????????????????????????????????????????????? [確定]
[root@fsailing1 ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.? Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.0.95 Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
MYSQL入門Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
MYSQL入門Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MYSQL入門mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
MYSQL入門Database changed
mysql> show create table test1;
| CREATE TABLE `test1` (
? `id` int(11) NOT NULL auto_increment,
? `name` varchar(10) default NULL,
? PRIMARY KEY? (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=<SPAN style="COLOR: #ff0000">9</SPAN> DEFAULT CHARSET=utf8 |
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