MySQL中index和key的关系

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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.

简言之，在MySQL中，INDEX和KEY的概念是一样的。PRIMARY KEY要求NOT NULL，其他KEY不要求。

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MySQL中index和key的关系

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原文地址：http://www.cnblogs.com/seasonzone/p/4210930.html