In the context of databases, "Integrity Constraints" refers to specific rules that are implemented to ensure the accuracy and consistency of the data within a relational database. These rules govern the data as it is inserted, updated, and deleted, thereby preventing undesirable data corruption and enforcing the desired logical structure. The definition of Integrity Constraints can be detailed further into several aspects:
Domain Integrity: This ensures that all entries in a given column are consistent and fall within a defined domain. For example, if a column is expected to have positive numbers, the domain constraint will prevent negative numbers or non-numeric values from being inserted.
Entity Integrity: This refers to the uniqueness of rows within a table, typically enforced through the use of primary keys. The primary key uniquely identifies a record in a table, and entity integrity ensures that no duplicate keys exist, thus maintaining the distinctness of each record.
Referential Integrity: This constraint ensures that relationships between tables remain consistent. When one table has a foreign key that is a reference to the primary key of another table, referential integrity ensures that this connection is maintained. If a record that is referred to by a foreign key is deleted or altered, the database will take defined actions, such as updating the referencing key or denying the change.
User-Defined Integrity: These constraints are specific to the business logic or rules that pertain to the particular use-case of the database. For example, a user-defined constraint might require that an employee's salary not exceed a certain amount or that a customer's age must be over 18. These rules can be tailored to the specific requirements of a given application.
Check Constraints: These constraints enable more specific rules to be defined for the data within a column or set of columns. For example, a check constraint might require that a percentage value must fall between 0 and 100 or that a date of birth entry must be earlier than the current date.
Null Constraints: This determines whether a null value can be allowed for a particular attribute. If a null constraint is applied to a column, it ensures that every row in that column must contain a value.
Temporal Integrity: This ensures the accuracy and consistency of date and time data within the database, often ensuring that date and time values follow logical sequences and adhere to defined formats.
Integrity Constraints play a crucial role in maintaining the reliability and robustness of a database system. They are typically defined during the database design phase and enforced by the database management system (DBMS).
Without proper integrity constraints, a database might suffer from inconsistencies, ambiguities, and errors that could significantly impact its usability and trustworthiness. These constraints, therefore, form an essential part of database architecture, ensuring that the data adheres to the expected rules and quality standards.
