What do you mean by database constraints?

Database constraints are rules used to restrict data in database tables, which help to ensure the integrity and consistency of data. Constraints can be divided into many types, such as primary key, foreign key, unique key, non-empty constraint, check constraint and so on. Constraints can prevent data pollution or damage caused by users' misoperation, and observing constraints can improve the quality and reliability of data.

Database constraints play an important role in database management and maintenance. First of all, it limits the input range of data, improves the accuracy and reliability of data, and is not prone to errors and contradictions. Secondly, constraints protect data security, prevent data loss and misuse, and avoid malicious attacks and illegal intrusions. Finally, constraints standardize the organization and storage of data, reduce the complexity and cost of data management and maintenance, and improve the efficiency and accuracy of data query and analysis.

Using database constraints requires designing and planning the structure and attributes of the table, defining key fields or attributes such as primary key, foreign key and unique key, and setting corresponding constraints. When data is entered, updated or deleted in the database, the integrity and consistency of the data will be automatically detected and verified. If the constraint conditions are not met, an error prompt will be generated or the operation will be rejected. Therefore, using constraints requires certain skills and experience, and grasping the scope and strength of constraints can achieve good results and security.