Relational Algebra / 关系代数符号可以用于表达数据库标准操作逻辑。近期做数据库作业时经常需要用 $\LaTeX$ 表示关系代数的符号，故在这里稍作整理。
| Operation | 中文 | 符号 | $\LaTeX$ |
|---|---|---|---|
| Projection | 投影 | $\Pi$ | \Pi |
| Selection | 选择 | $\sigma$ | \sigma |
| Renaming | 重命名 | $\rho$ | \rho |
| Aggregate Function | 聚合函数 | $\mathcal{G}$ | \mathcal{G} |
| Union | 交 | $\cap$ | \cap |
| Intersection | 补 | $\cup$ | \cup |
| Natural Join | 自然连接 | $\bowtie$ | \bowtie |
| Left Outer Join | 左外连接 | ⟕ | … 这几个直接复制吧 |
| Right Outer Join | 右外连接 | ⟖ | |
| Full Outer Join | 全外连接 | ⟗ | |
| Cartesian product | 笛卡尔乘积 | $\times$ | \times |
| Divide | 除 | $\div$ | \div |
| Assignment | 赋值 | $\leftarrow$ | \leftarrow |
| And | 条件并列 | $\land$ | \land or \vee |
| Negation | 非 | $\neg$ | \neg |
| Exist | 存在 | $\exists$ | \exists |
| For All | 对所有 | $\forall$ | \forall |
| 下标文字 | $\sigma_{\text{username}}$ | _{\text{}} |
|
| 粗体文字 | $\mathcal{G}_{\textbf{count(*)}}$ | \textbf{} |
|
| 长长长长括号 | $\big( \Big( \bigg( \Bigg($ | \big( \Big( \bigg( \Bigg( |
|
| 比较 | $\gt \ge \lt \le \ne$ | \gt \ge \lt \le \ne |
一个栗子🌰：
c\leftarrow \Pi_{count}\Big(\sigma_{\text{publisher="McGraw-Hill"}}(_{publisher,} \mathcal{G}_{\textbf{count(*) as count}}(books))\Big) \\
t\leftarrow _{name,}\mathcal{G}_{\textbf{count(*) as memcount}}(\sigma_{\text{publisher="McGraw-Hill"}}(member \bowtie borrowed\bowtie books)) \\
\Pi_{name}(\sigma_{\text{memcount=c}}(t))
$$c\leftarrow \Pi_{count}\Big(\sigma_{\text{publisher=‘McGraw-Hill’}}(_{publisher,} \mathcal{G}_{\textbf{count(＊) as count}}(books))\Big)$$
$$t \leftarrow_{name,} \mathcal{G}_{\textbf{count(＊) as memcount}} (\sigma_{\text{publisher=‘McGraw-Hill’}}(member \bowtie borrowed\bowtie books))$$
$$\Pi_{name}(\sigma_{\text{memcount=c}}(t))$$