February 2024
Intermediate to advanced
370 pages
7h
Chinese
Content preview from 数据工程之道：设计和构建健壮的数据系统
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查询、建模和转换
|
267
行。最后，事实表不引用其他事实表，它们只引用维度。
让我们看一下一个基本事实表的例子（如表
8-9
所示）。在你的公司中，一个常见的问题
可能是这样的：显示每个客户每天每个订单的销售总额。事实表应该是细粒度的
—
在
这个例子中需要包含销售的订单
ID
、客户、日期和销售总额。注意，事实表中的数据类
型都是数字（整数和浮点数），没有字符串。在这个例子中，
Customer Key
等于
7
的用
户在同一天有两个订单，这反映了表的粒度。相反，事实表的键引用了不同的维度表，
如客户和日期信息等。销售总额代表销售
事件
的总销售额。
表 8-9：一个基本事实表
OrderID CustomerKey DateKey GrossSalesAmt
100 5 20220301 100.00
101 7 20220301 75.00
102 7 20220301 50.00
维度表
。
Kimball
数据模型中的第二种类型的表是
维度表
。维度表为存储在事实表中的
事件提供参考数据、属性和关系上下文。维度表比事实表小（形状相反），通常是宽而
短。当连接到事实表时，维度可以描述事件的内容、地点和时间。维度是去范式化的，
有可能出现重复的数据。这在
Kimball
数据模型中是允许的。让我们来看看前面事实表
例子中提到的两个维度。
在
Kimball
数据模型中，日期通常被存储在一个日期维度中，允许你在事实和日期维度
表之间引用日期键（
DateKey
）。通过日期维度表，你可以很容易地回答这样的问题：“我
在
2022
年第一季度的总销售额是多少 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.