What does a check constraint in SQL ensure?

A check constraint in SQL is a rule that specifies a condition that must be met for the data in a specific column of a table. By enforcing certain criteria, a check constraint ensures that only valid data values are allowed in that particular column. For example, if you have a column that should only accept positive integers, a check constraint can be added to enforce that rule. This helps maintain data integrity by preventing invalid entries that do not comply with the specified condition.

This concept is distinct from other elements of database structure and management. While check constraints ensure data validity, they do not dictate the overall structure of the database, which would involve table definitions and relationships among tables. Data types are defined separately and ensure that the data conforms to a specified type, but they do not limit values to specific conditions. Relationships between tables, such as those established using foreign keys, focus on how tables interact with one another, rather than restricting values within a single column of a table.