The information contained in these pages is normally sufficient, coupled with the IBEasy+ software and the Firebird DBMS, to build and query relational databases.
However, the reader wishing to deepen, or complete, this training will find below various links in order to achieve these objectives.
Many references, both in terms of books and websites, are in English. This is due to the fact that most of the developments on databases and SQL have been done and are still done in the English language. It is therefore important to work on the original documents and not on translations or adaptations. This is especially true for books dealing with database design.
When it comes to websites for learning SQL, the vast majority of those listed below allow for interactive language learning. This is actually the best way to learn SQL.

Databases Design Autors
Relational Model Database Management 2  E. F. Codd
An Introduction to Database Systems - Vol. 2 C. J. Date
Database Design and Relational Theory: Normal Forms and All That Jazz C. J. Date
BASES DE DONNEES. Les systèmes et leurs langages G. Gardarin
Schaum's Outline of Fundamentals of Relational Databases R. Mata-Toledo
Modélisation Conceptuelle de Données - Une Démarche Pragmatique P. Bergougoux
SQL and Relational Theory: How to Write Accurate SQL Code C. J. Date
Schaum's Outline of Fundamentals of SQL Programming R. Mata-Toledo
SQL R. Plew
SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL  John L. Viescas
Instant SQL Programming Joe Celko
SQL websites  
SQL Course (Not interactive site)