在关系代数中等同于GroupBy和Having子句 [英] Equivalent of GroupBy and Having clause in Relational Algebra

问题描述

我正在做一个任务，我不得不将SQL查询转换为关系代数查询。我遇到了转换组子句。

I was doing an assignment where I had to convert SQL queries into Relational Algebra queries. I got stuck in converting the group by clause.

任何人都可以告诉我如何group by子句以关系代数写？

Could anyone please tell me how the group by clause can be written in relational algebra?

例如：

SELECT job, sal 
  FROM emp
 GROUP BY job
       ;

$ b

谢谢！

Thanks!

推荐答案

首先你的查询是错误的，你不能选择你没有分组，除非你使用聚合。我假设你想得到sal的总和。

First of all your query is wrong you cannot select something that you did not group unless you use aggregation. I assume you want to get sum of the sal.

job F sum（sal），job（emp）。

job F sum(sal), job(emp).

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