选择和项目运营有什么区别 [英] What is the difference between Select and Project Operations

问题描述

我在这里指的是基本的关系代数运算符.
正如我所看到的，项目可以完成的所有事情都可以通过select来完成.

I'm referring to the basic relational algebra operators here.
As I see it, everything that can be done with project can be done with select.

我不知道我是否错过了任何区别或细微差别.

I don't know if there is a difference or a certain nuance that I've missed.

推荐答案

选择操作:该操作用于从指定给定逻辑的表(关系)中选择行，称为predicate.谓词是用户定义的条件，用于选择用户选择的行.

Select Operation : This operation is used to select rows from a table (relation) that specifies a given logic, which is called as a predicate. The predicate is a user defined condition to select rows of user's choice.

项目操作:如果用户有兴趣选择一些属性的值，而不是选择表(关系)的所有属性，则应该进行PROJECT操作.

Project Operation : If the user is interested in selecting the values of a few attributes, rather than selection all attributes of the Table (Relation), then one should go for PROJECT Operation.

查看更多信息:关系代数及其操作

这篇关于选择和项目运营有什么区别的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！