mysql数据库引擎MyISAM和InnoDB的比较和使用场合
数据库中数据管理的一种方式，MySQL支持插入式的存储引擎，也就是说你同一数据库中的数据表可以选择不同存储引擎
查看mysql版本
mysql> select version();
+-----------+
| version() |
+-----------+
| 5.5.25a |
+-----------+
1 row in set
查看mysql引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
mysql5.5版本默认的数据库引擎是innoDB
最常见的数据库引擎是InnoDB和MyISAM
MyISAM
ISAM执行读取操作的速度很快，而且不占用大量的内存和存储资源。ISAM的两个主要不足之处在于，它不 支持事务处理，也不能够容错，MyISAM除了提供ISAM里所没有的索引和字段管理的大量功能，MyISAM还使用一种表格锁定的机制，来优化多个并发的读写操作，其代价是你需要经常运行OPTIMIZE TABLE命令，来恢复被更新机制所浪费的空间。MYISAM强调了快速读取操作。
InnoDB
在使用MYSQL的时候，你所面对的每一个挑战几乎都源于ISAM和MyISAM数据库引擎不支持事务处理（transaction process）也不支持外来键。尽管要比ISAM和 MyISAM引擎慢很多，但是InnoDB包括了对事务处理和外来键的支持，这两点都是前两个引擎所没有的。
两种引擎的比较与使用场合
MyISAM类型不支持事务处理等高级处理，而InnoDB类型支持。
MyISAM类型的表强调的是性能，其执行数度比InnoDB类型更快，但是不提供事务支持，而InnoDB提供事务支持已经外部键等高级数据库功能。
MyISAM格式的一个重要缺陷就是不能在表损坏后恢复数据
InnoDB 中不保存表的具体行数，也就是说，执行select count(*) from table时，InnoDB要扫描一遍整个表来计算有多少行，但是MyISAM只要简单的读出保存好的行数即可。注意的是，当count(*)语句包含where条件时，两种表的操作是一样的
MyISAM的索引和数据是分开的，并且索引是有压缩的，内存使用率就对应提高了不少。能加载更多索引，而Innodb是索引和数据是紧密捆绑的，没有使用压缩从而会造成Innodb比MyISAM体积庞大
DELETE FROM table时，InnoDB不会重新建立表，而是一行一行的删除
MyISAM适合：
(1)做很多count 的计算；
(2)插入不频繁，查询非常频繁；
(3)没有事务。
InnoDB适合：
(1)可靠性要求比较高，或者要求事务；
(2)表更新和查询都相当的频繁，并且表锁定的机会比较大的情况指定数据引擎的创建
更改一个表的数据库引擎
查看表结构
mysql> describe cds;
+-----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+----------------+
| titel | varchar(200) | YES | | NULL | |
| interpret | varchar(200) | YES | | NULL | |
| jahr | int(11) | YES | | NULL | |
| id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
+-----------+---------------------+------+-----+---------+----------------+
4 rows in set查看建表语句
mysql> show create table cds;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| cds | CREATE TABLE `cds` (
`titel` varchar(200) COLLATE latin1_general_ci DEFAULT NULL,
`interpret` varchar(200) COLLATE latin1_general_ci DEFAULT NULL,
`jahr` int(11) DEFAULT NULL,
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=7 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set查看表的详细信息
mysql> show table status like 'cds';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+
| 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 |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+
| cds | MyISAM | 10 | Dynamic | 3 | 49 | 176 | 281474976710655 | 2048 | 28 | 7 | 2005-10-25 15:47:49 | 2012-04-16 23:30:18 | NULL | latin1_general_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+
1 row in set修改数据库引擎
mysql> alter table cds engine=InnoDB;
Query OK, 3 rows affected
Records: 3 Duplicates: 0 Warnings: 0再次查看表的详细信息
mysql> show table status like 'cds';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-------------------+----------+----------------+---------+
| 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 |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-------------------+----------+----------------+---------+
| cds | InnoDB | 10 | Compact | 3 | 5461 | 16384 | 0 | 0 | 6291456 | 7 | 2012-04-16 23:30:18 | NULL | NULL | latin1_general_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-------------------+----------+----------------+---------+