Online computer courses, code, programming tutorial and sidebar information for monitoring Canadian S&P/TSX index. Build friendship and networking. Welcome to visit my blogs often!!! I also have two other sites: YouTube Channel and Google site.
Adsense
Popular Posts
- PHPWind-- A PHP forum script applcaition in China
- Using Cron Job to process PHP scripts
- Install PHPMailer 5.2.4 and use smtp gmail
- Datatable export excel wraptext and newline
- PHP connect IBM db2 database in XAMPP
- Sweet Alert JS library - beautiful replacement of JavaScript Alert
- PHP - Export Content to MS Word document
- PHP: add a download as pdf file button in report page
- Using JS Chosen library for multiselect dropdown
- phpexcel toggle expand and hide column in EXCEL and summary
Tuesday, April 23, 2013
Difference between PRIMARY KEY, UNIQUE KEY and key in MySQL
Primary key, unique key and key in MySQL are used as index to speed up search process.
Primary key and unique key can not have same values for two distinct rows, while key will not require this. There is only one primary key in one table, but can have several unique keys.
Example:
CREATE TABLE member` (
`member_id` mediumint(8) unsigned NOT NULL auto_increment,
`login` varchar(20) NOT NULL default '',
`password` varchar(20) NOT NULL default '',
`email` varchar(50) NOT NULL default '',
`country` varchar(50) NOT NULL default '',
`phone` varchar(15) NOT NULL default '',
`extension` varchar(10) NOT NULL,
`creation_date` datetime NOT NULL default '0000-00-00 00:00:00',
`membership_type` tinyint(4) NOT NULL default '0',
`last_login` datetime NOT NULL default '0000-00-00 00:00:00',
`account_control` tinyint(4) NOT NULL default '1',
`dept_id` mediumint(8) unsigned NOT NULL default '0',
`organization` varchar(255) NOT NULL,
`site` varchar(255) NOT NULL,
`unit` varchar(255) NOT NULL,
`manager` varchar(255) NOT NULL,
`language` varchar(5) NOT NULL default 'en',
`preferences` text NOT NULL,
PRIMARY KEY (`member_id`),
UNIQUE KEY `login` (`login`),
KEY `email` (`email`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
PRIMARY KEY (`member_id`): index name and kind are primary, using column member_id
UNIQUE KEY `login` (`login`): index name login and kind unique using column login
KEY `email` (`email`) index name email, index kind: index, using column email.
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment