SQL ET POSTGRE 2.2 : What is a relational database and SQL

In this video we look at what a relational database is, what a database management system does and how SQL fits into the picture. In a database, data is stored in tables. Tables are similar to Excel sheets — they are made of columns and rows of data — and they can be linked together through relationships. These relationships between tables are what make a relational database so powerful: they let us identify a piece of data that is linked to another piece of data elsewhere in the database.

An example of a relation

Imagine a table of pets containing a few columns: an id column to uniquely identify each animal, a type column (cat, dog, etc.), a name column, an age column, and an owner_id column used to link the pets table to a second table. The other table is the owners table, which stores each owner's first name, last name, age and city of residence. The first column there is also an id. The id column of the owners table is linked to the owner_id column of the pets table, so we can tell who owns which pet — Moustache the cat belongs to Audrey from Lille, Snoopy the dog and Carotte the rabbit both belong to Marion. We will explore relations in much more depth later in the course.
  • RDBMS = Relational Database Management System (MySQL, Oracle, SQL Server, PostgreSQL).
  • SGBDR in French = the exact same concept.
  • SQL is the language used to talk to any RDBMS.
When people talk about databases, they usually mean a relational database management system, or RDBMS. All the popular databases — MySQL, Oracle SQL, SQL Server — are in fact RDBMSs. They provide tools and graphical interfaces to interact with the data. PostgreSQL is the relational database we will use throughout this course; it is one of the most powerful and popular in the world. SQL itself is the language used to talk to relational databases: we write queries to create tables, insert, update, delete and retrieve data. SQL syntax is very similar across systems, so what you learn here also applies to MySQL, Oracle and the rest. Next we will install PostgreSQL.

Summary

This lesson introduces relational databases as systems that store data in interconnected tables composed of columns and rows. It explains how relationships between tables enable powerful data associations—such as linking pet owners to their animals—and introduces the core concepts of RDBMS (Relational Database Management Systems) and SQL (Structured Query Language), the universal language for querying relational databases like PostgreSQL.

Key points

  • Relational databases store data in tables with columns and rows, similar to Excel spreadsheets
  • Relationships between tables allow you to connect and link data across different tables in a database
  • RDBMS (Relational Database Management System) provides the tools and interface to interact with relational databases
  • SQL (Structured Query Language) is used to create tables, insert data, modify data, and retrieve information from relational databases
  • SQL syntax is similar across different RDBMS platforms (MySQL, Oracle, PostgreSQL), making knowledge transferable
  • PostgreSQL is one of the most powerful and popular relational databases in the world

FAQ

What is a relational database?

A relational database is a database where data is stored in tables composed of columns and rows. Tables can be linked together through relationships, allowing data in different tables to be associated and queried together.

How do relationships work in a relational database?

Relationships connect tables by using columns that reference primary keys in other tables. For example, a pets table can reference an owners table through an owner ID column, allowing you to see which owner has which pet.

What is SQL and what is its role?

SQL (Structured Query Language) is the language used to interact with relational databases. It allows you to create tables, insert data, modify existing data, retrieve information, and perform many other database operations.