Database Chapter 2 Relational database

Chapter II Relational databases

Relational database is the most important and most widely used database system.

This chapter focuses on the basic concepts of relational models, namely, the data structure of relational models, the relationship operations and the integrity of relationships.

There are three types of integrity constraints in a relational model: entity integrity, referential integrity, and user-defined integrity. The first two constraints are the integrity constraints that the relational model must satisfy, which is called the two invariance of the relationship, which should be automatically supported by the relational system, and the user-defined integrity is the constraint condition that the application domain needs to obey, which embodies the semantic constraints in the specific domain.

Entity integrity: A cannot be null if attribute A is the primary attribute of the basic relationship R.

Referential integrity:

Database Chapter 2 Relational database