Databases Course - Relational Model - NULL Values in SQL | Database Tutorial 2d

In this lecture of the databases course we learn about NULL values in the relational model. When dealing with NULL values it is crucial to understand that SQL uses a three-valued logic: any comparison with NULL results in unknown (even NULL = NULL is not true in SQL). We will also see that SQL allows to declare attributes as not nullable (NOT NULL). This is the databases online course given at the Vrije Universiteit Amsterdam by Jörg Endrullis. The course objective is to obtain a good understanding of relational database systems from the user perspective. This includes the ability to develop conceptual database models, as well as key concepts and skills in relational database theory and practice. Among others, we treat in this course the following subjects: (a) entity–relationship diagrams for the design of database schemata, (b) the relational database model and integrity constraints, (c) SQL (structured query language) for retrieving information from relational databases, (d) database normalisation and functiona dependencies (reasoning about good database design), (e) transactions and concurrency control. The slides are based on work by Peter Boncz and Torsten Grust.