mysql主键必定是唯一索引------顺便用实例说说索引的创建

  创建表：

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1. CREATE TABLE `tbtest` (      
2.   `id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY COMMENT 'student id',      
3.   `name` VARCHAR(32) NOT NULL COMMENT 'student name',      
4.   `score` INT UNSIGNED NOT NULL DEFAULT '0' COMMENT 'student score'    
5. ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COMMENT='student tb'  

        看下：

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1. mysql> show create table tbtest;  
2. +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
3. | Table  | Create Table                                                                                                                                                                                                                                                                                                |  
4. +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
5. | tbtest | CREATE TABLE `tbtest` (  
6.   `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'student id',  
7.   `name` varchar(32) NOT NULL COMMENT 'student name',  
8.   `score` int(10) unsigned NOT NULL DEFAULT '0' COMMENT 'student score',  
9.   PRIMARY KEY (`id`)  
10. ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='student tb' |  
11. +--------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
12. 1 row in set (0.00 sec)  

       显然：mysql主键是唯一索引。

       我们来为name创建索引， 如下：

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1. mysql> ALTER TABLE `tbtest` ADD INDEX idx_name (`name`) ;  
2. Query OK, 0 rows affected (0.16 sec)  
3. Records: 0  Duplicates: 0  Warnings: 0  
4.   
5. mysql> show create table tbtest;                           
6. +--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
7. | Table  | Create Table                                                                                                                                                                                                                                                                                                                           |  
8. +--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
9. | tbtest | CREATE TABLE `tbtest` (  
10.   `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT 'student id',  
11.   `name` varchar(32) NOT NULL COMMENT 'student name',  
12.   `score` int(10) unsigned NOT NULL DEFAULT '0' COMMENT 'student score',  
13.   PRIMARY KEY (`id`),  
14.   KEY `idx_name` (`name`)  
15. ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='student tb' |  
16. +--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+  
17. 1 row in set (0.00 sec)  

        顺便来小结一下各类索引的创建：

       1. 添加PRIMARY KEY（主键索引， 一般来说， 如果设置为主键后， 它自动会成为索引， 不需要再设置） 

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1. ALTER TABLE `table_name` ADD PRIMARY KEY ( `column` );   

       2. 添加UNIQUE(唯一索引) 

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1. ALTER TABLE `table_name` ADD UNIQUE ( `column` ) ;  

       3. 添加INDEX(普通索引) 

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1. ALTER TABLE `table_name` ADD INDEX index_name ( `column` ) ;  

       4. 添加FULLTEXT(全文索引) 

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1. ALTER TABLE `table_name` ADD FULLTEXT ( `column`) ;  

       5. 添加多列索引 (实际上就是捆绑索引)

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1. ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` );  

       简单， 不多说。