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update translation in chapter 2

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Gang Yin 2023-02-16 21:36:35 +08:00
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@ -315,13 +315,13 @@ function getSharks() {
}
```
在关系代数中：
而在关系代数中，你可以这样写：
$$
sharks = \sigma_{family = "sharks"}(animals)
$$
$\sigma$（希腊字母西格玛）是选择操作符，只返回符合条件的动物，`family="shark"`。
其中 $\sigma$（希腊字母西格玛）是选择操作符，只返回符合 `family="shark"` 条件的动物。
定义 SQL 时，它紧密地遵循关系代数的结构：