Zoo

It would be a lot easier to keep track of all these animals if we have a database of them. I'll bet the real zoos do that too. Keep record of all of these animals that live there, and what they need to eat, and so on. Let's see how we might do that.

我們這裡來舉一個動物園的例子，動物園會需要一個資料庫來記錄動物的名字與飲食習慣等資料，我們來試著做做看。

So using the data in the animal's table, try answering these questions. About the third question, nothing in this table tells us anything about the family relationships between gorillas so we can't answer the third question. We left it in blank. The other three questions we can answer from the table. Whenever we look for an answer that combines the values from several rows. Whether by counting them or adding up numerical values, or finding the average, we're doing what's called aggregation. Counting is the simplest aggregation there is.

只有第三個問題在 table 裡找不到，其他問題都可以找到或是用數的算出來。這些算數或是找平均數的動作我們稱做 aggregation。

備註：llama(美洲駝)