SQL ET POSTGRE 3.5 : Single constraints not null and check

The unique not null and check constraints are essential tools in the creation of reliable and efficient databases. The unique constraint ensures that each value in a column is unique, preventing duplicate entries and data entry errors. The not null constraint ensures that each record contains a value for that column, preventing missing data. The check constraint ensures that the values in a column meet a specific criterion, such as the range of values allowed or the validity of a format. The use of these constraints is crucial to the quality of the data stored in a database, which can have a direct impact on the performance and reliability of the application that uses the data. Indeed, the constraints make it possible to guarantee the integrity of the data, to avoid input errors and to facilitate search and sorting operations. In terms of natural referencing (SEO), the use of these constraints can also have a positive impact on the ranking of web pages. Indeed, a well-structured and optimised database can improve the speed of page loading, which is an important factor for SEO. In addition, a well-organised database can facilitate the indexing of pages by search engines, which can improve the visibility and ranking of web pages.