INNER join 等价于 join
你可以理解为 join 是 INNER JOIN 的缩写。
left JOIN 等价于 left OUTER JOIN
right JOIN 等价于 RIGHT OUTER JOIN
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http://zhidao.baidu.com/link?url=0GN239DZY8SCTEibvjel2iUjnZtm00tRWOenK58mEH8hqPuyMOOlE1gXxcGcAWs9oUxX9q7M9R12P-HamD0nca
原文：http://www.cnblogs.com/qinqiu/p/4702812.html