虽然规范的示例使用矢量表达作为键和值，但是并没有限制您如何来定义值(例如一些值的汇总)。
Although canonical examples use the vector representation as a key and value, there's no restriction on how you can define the value (such as an aggregate of a number of values).
内部矢量中的第一项是键（本例中为 movie-title），第二项是值（本例中是一个表示放映时间的整数）。
The first item in the inner vector is the key (in this case, movie-title), and the second is the value (in this case, an integer representing the running time).
如果查询编辑器在表之间找不到外键关系，则缺省设置为矢量积。
If it cannot find a foreign key relationship between the tables, the default is a cross product.
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