Conceptual

Relational database management systems allow you to control what data gets added to a table with constraints. A constraint is a special rule that applies to one or more columns — or to an entire table — that restricts what changes can be made to a table’s data. This article will go over in detail what constraints are and how they’re used in relational databases. It will also walk through each of the five constraints defined in the SQL standard and explain their respective functions.

SQL (Structured Query Language) defines, manipulates, and queries data held in relational databases. SQL is used in many industries and with the most popular tools. Even if you don’t use SQL directly, you can still benefit from understanding its concepts. This conceptual article outlines why it’s worth learning SQL and reviews where and how you can apply that knowledge.