Databases and SQL

This book describes what databases are and how they can be designed. The book also describes how to make queries with which the data in a relational database can be retrieved with the use of SQL. The first half of ‘Databases and SQL’ discusses what a database is, the essence of what a database management system is, the place of database technology in system development and the relational model on which relational databases are based. The book gives definitions of the concepts of the relational model, it shows the way a relational database is designed, how to verify the design of a relational database and how to implement a relational database with the use of SQL. The second half of the book shows how to retrieve data from a relational database with the use of queries. There are separate chapters for the development of queries with joins, for the use of GROUP BY / HAVING and for the use of subqueries. The use of subqueries is split up in a chapter for the use of subqueries without correlation, a chapter for the use of subqueries with correlation and a chapter that explains how [NOT] EXISTS can be used in subqueries for group-group comparisons.