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mysql中的auto_increment的问题 今儿在逛论坛时,发现一个看似很简单的问题,却引起了大家的广泛关注:这是一道很早的面试题:
一张表,里面有ID自增主键,当insert了17条记录之后,删除了第15,16,17条记录,再把Mysql重启,
再insert一条记录,这条记录的ID是18还是15 。 答案:如果表的类型是MyISAM,那么是18。 因为MyISAM表会把自增主键的最大ID记录到数据文件里,重启MySQL自增主键的最大ID也不会丢失。 如果表的类型是InnoDB,那么是15。 InnoDB表只是把自增主键的最大ID记录到内存中,所以重启数据库或者是对表进行OPTIMIZE操作,
都会导致最大ID丢失。 自己也做了个实验,结果证实了上面的说法。真是惭愧啊,看似简单的问题自己也打错了。[html]mysql> select * from test1; +----+-----------+ | id | name | +----+-----------+ | 1 | 陈兵辉 | | 2 | chen | | 3 | chen | | 4 | chen | | 5 | chen | | 6 | chen | | 7 | chen | | 8 | chen | | 9 | chen | | 10 | chen | | 11 | chen | +----+-----------+ 11 rows in set (0.00 sec) mysql> delete from test1 where id in (10,11,9); Query OK, 3 rows affected (0.03 sec) 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=12 DEFAULT CHARSET=utf8 | mysql> exit; Bye [root@fsailing1 ~]# service mysqld restart 停止 MySQL: [确定] 启动 MySQL: [确定] [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. 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 test; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A 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=9 DEFAULT CHARSET=utf8 |
2,另外还有一个就是获取当前数据库表的自增字段数。[html]mysql> select last_insert_id(); +------------------+ | last_insert_id() | +------------------+ | 0 | +------------------+ 1 row in set (0.00 sec) 作者 chen861201 bitsCN.com

InnoDBBufferPool reduces disk I/O by caching data and indexing pages, improving database performance. Its working principle includes: 1. Data reading: Read data from BufferPool; 2. Data writing: After modifying the data, write to BufferPool and refresh it to disk regularly; 3. Cache management: Use the LRU algorithm to manage cache pages; 4. Reading mechanism: Load adjacent data pages in advance. By sizing the BufferPool and using multiple instances, database performance can be optimized.

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

MySQL is worth learning because it is a powerful open source database management system suitable for data storage, management and analysis. 1) MySQL is a relational database that uses SQL to operate data and is suitable for structured data management. 2) The SQL language is the key to interacting with MySQL and supports CRUD operations. 3) The working principle of MySQL includes client/server architecture, storage engine and query optimizer. 4) Basic usage includes creating databases and tables, and advanced usage involves joining tables using JOIN. 5) Common errors include syntax errors and permission issues, and debugging skills include checking syntax and using EXPLAIN commands. 6) Performance optimization involves the use of indexes, optimization of SQL statements and regular maintenance of databases.

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA


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