It is used when there are no indexes on one or more joining tables, or when the database server must read a large number of rows from all joining tables.
当一个或多个连接表上没有索引时，或者当数据库服务器必须从所有连接表中读取大量行时，就使用这种方法。
It is more like a digital news-stand than a personalised magazine: users can subscribe to various publications, but must read each one separately instead of seeing all their stories together.
它看起来更像是一个数字杂志摊而并非个性化定制的杂志，读者可以向不同的出版商订阅电子杂志，但每次只能读到其中一篇文章而不是读照单全读。
It takes just seconds to read an E-mail or a politician's tweet. One must make some heroic assumptions about the appeal of digital media to think they influence people as much as traditional outlets.
要想认为数字媒体同传统媒体拥有同等的影响力，他不得不就其吸引力做出巨大的假设。
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