In this case, you want to restrict the definition of a Pamphlet, which is similar to a Book in every way except that it has no author.

在本例中，希望限制Pamphlet(小册子)的定义，除了没有作者以外，它与Book完全相似。

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Since this query contains no value predicate to restrict either the books or the authors table, DB2 has to perform a table scan on either of the two tables to read all author IDs.

由于该查询没有包含用来限制books或authors表的值谓词，因此DB 2必须在两个表上执行表扫描，以便读取所有author ID。

youdao

You can also restrict the posts by author.

你也可以根据作者限制文章数目。

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