Can you list the main limitations that exist for tables in databases?

Constraints for tables in databases ensure data integrity and correctness. They include:

• PRIMARY KEY — a unique identifier for each record, does not allow NULL.
• FOREIGN KEY — maintains referential integrity between tables, linking records to another table.
• UNIQUE — guarantees the uniqueness of values in a column or set of columns.
• NOT NULL — prohibits NULL values in the specified column.
• CHECK — sets a condition that values in the column must satisfy.

For example, in a users table, you can specify that the email must be unique and not empty, and the age must be a positive number.