What is the relationship between DER and relational database?

DER or Entity-Relationship Diagram, as the name itself says, is a graphical representation of the entities needed in a data model and its relationships, so it is an abstract form.

Relational databases are the mechanisms that deliver these representations and produce a database with these entities and have facilities that allow them to be accessed in a related way.

Precisely because both are based on the relationship of the data they fit well.

It is common to say that the DER is used to create a logical model and the database is the physical model. It's a bit more complicated than that, but it's a simplified way to understand.

The database is the implementation of what was specified in the DER.

A entity relationship model (MER) describes the objects (entities) involved in a business domain, with their characteristics (attributes) and how they relate to each other (relationships). This conceptual model is represented graphically by the relationship entity diagram (ER or DER). This diagram facilitates communication between team members as it provides a common language used by both the analyst, responsible for raising the requirements, and the developers, responsible for implementing what was modeled.

Already a relational database models the data in a way that they perceive the user as tables, or more formally relationships. The default language for Relational Databases is Structured Query Language , or simply SQL, as it is best known.

The relationship between RSI and relational database is that an ER model is usually implemented as a database. In cases of a relational database, which stores data in tables, the tables themselves represent the entities. Some data fields in these tables point to indexes in other tables, which represent relationships.

The DER is the diagram of entities and relationships ie you will show the part of it as the entities (tables) of your database are related would be a logical way of representing that relationship, and the relational database a form physics.

In general in the DER you put several entities relating, for example, product table with the supplier, product having only one supplier and the supplier several things, the relational model is the same thing, but with its direct application in the database already, through the primary and foreign keys.