[mysql] MySQL - Meaning of "PRIMARY KEY", "UNIQUE KEY" and "KEY" when used together while creating a table

Can anyone explain about the purpose of PRIMARY KEY, UNIQUE KEY and KEY, if it is put together in a single CREATE TABLE statement in MySQL?

CREATE TABLE IF NOT EXISTS `tmp` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `uid` varchar(255) NOT NULL,
  `name` varchar(255) NOT NULL,
  `tag` int(1) NOT NULL DEFAULT '0',
  `description` varchar(255),
  PRIMARY KEY (`id`),
  UNIQUE KEY `uid` (`uid`),
  KEY `name` (`name`),
  KEY `tag` (`tag`)
) ENGINE=InnoDB AUTO_INCREMENT=1 ;

How do I convert this query to MSSQL?

Just to add to the other answers, the documentation gives this explanation:

• KEY is normally a synonym for INDEX. The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. This was implemented for compatibility with other database systems.

• A UNIQUE index creates a constraint such that all values in the index must be distinct. An error occurs if you try to add a new row with a key value that matches an existing row. For all engines, a UNIQUE index permits multiple NULL values for columns that can contain NULL.

• A PRIMARY KEY is a unique index where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY. The name of a PRIMARY KEY is always PRIMARY, which thus cannot be used as the name for any other kind of index.

MySQL unique and primary keys serve to identify rows. There can be only one Primary key in a table but one or more unique keys. Key is just index.

for more details you can check http://www.geeksww.com/tutorials/database_management_systems/mysql/tips_and_tricks/mysql_primary_key_vs_unique_key_constraints.php

to convert mysql to mssql try this and see http://gathadams.com/2008/02/07/convert-mysql-to-ms-sql-server/