Can you list and explain the restrictions that can be applied to systems or databases?

Constraints in systems and databases are rules or conditions that restrict or control the behavior of data and operations with them. Main types of constraints:

• Data integrity: ensures correctness and consistency of data. For example, uniqueness constraint (UNIQUE), primary key (PRIMARY KEY), foreign keys (FOREIGN KEY).
• Data type constraints: define what data types can be stored in a column (e.g., INTEGER, VARCHAR).
• Size constraints: limit the amount of data, such as maximum string length.
• Access constraints: rights and roles that restrict who can perform what operations.
• Performance constraints: limits on the number of concurrent connections, query execution time.
• Transactional constraints: ensure atomicity, consistency, isolation, and durability (ACID).

Example: in a database, you can set a constraint that the email field must be unique to prevent duplication of users.