Soft questions: Relational algebra

First of all, from the macroscopic understanding of the concept of relational calculus, in other words is what is the relational algebra, which is my first work in touch with something. We all know that the database operation language of relational database is divided into two kinds: query and update. The query language is divided into relational algebra language and relational calculus language. This is about relational algebra. So it can be defined that relational algebra is the set operation of queries for database manipulation languages.

The operations in relational algebra can be divided into two categories

(1) Traditional set operation: And, Difference, intersection, Cartesian product, division.

(2) Expanded relational operation: projection, selection, connection,.

Common symbols

The five basic relational algebra

1, and

A relationship R and S have the same relational pattern, and R and S are made up of a set of tuples that belong to R or S, and are recorded as R∪s. The form is defined as follows:

R∪s≡{t | T∈r∨t∈s},t is a tuple variable, the number phase of R and S