Describe Integrity Constraints.
Integrity constraints are rules or conditions that are defined and enforced on a database, in order to maintain data integrity and consistency. These constraints act as safeguards to ensure that data stored in the database meets certain criteria or conditions, preventing any inconsistent or invalid data from being inserted, updated, or deleted.
Integrity constraints can be divided into various types:
1. Domain constraints: These constraints define the allowed values for a particular attribute in a database table. For example, a domain constraint on a "gender" attribute may allow only two values - "male" or "female".
2. Key constraints: These constraints ensure that each record in a table has a unique identifier or key value. It can be a primary key constraint, which enforces uniqueness and non-nullability of a primary key attribute, or a unique key constraint, which enforces uniqueness on a non-primary key attribute.
3. Referential integrity constraints: These constraints maintain the consistency between related tables. For example, a foreign key constraint ensures that a value in a column of one table matches a value in the primary key column of another related table.
4. Entity integrity constraints: These constraints govern the primary key attribute(s) of a table, ensuring that it is unique and non-null.
5. Check constraints: These constraints validate the values that are entered or updated in a column against a predefined condition or expression. For example, a check constraint can restrict the age column to accept values between 18 and 65.
By enforcing these integrity constraints, databases can prevent data inconsistencies, maintain data accuracy and validity, and enhance the overall reliability and quality of the data stored within.
Define and Describe different types of Integrity Constraints.
1. Domain Constraints: Domain constraints define the permissible values for an attribute in a database table. They ensure that data entered into a column adheres to a predefined set of values. For example, a domain constraint on a "color" attribute may specify that the allowed values are "red," "blue," or "green," and any attempt to insert a different value would be rejected.
2. Key Constraints: Key constraints ensure the uniqueness and non-nullability of a primary key attribute in a table. A primary key constraint enforces that each record in a table has a unique identifier. It prevents duplicate or null values in the primary key column. Unique key constraints function similarly but are applied to non-primary key attributes.
3. Referential Integrity Constraints: Referential integrity constraints enforce the consistency and relationships between related tables. They are based on foreign key and primary key relationships. For example, a referential integrity constraint ensures that a value in a foreign key column matches a value in the referenced primary key column of another table. It prevents orphaned records and maintains data integrity in relational databases.
4. Entity Integrity Constraints: Entity integrity constraints govern the primary key attribute(s) of a table. They ensure that the primary key is unique and non-null for each record in the table. These constraints help maintain the uniqueness and identity of individual records.
5. Check Constraints: Check constraints validate the values entered or updated in a column against a predefined condition or expression. They define a logical condition that must be met for the data to be considered valid. For example, a check constraint can restrict the age column to accept values between 18 and 65, preventing the entry of invalid ages.
By utilizing these different types of integrity constraints, databases can ensure that the data stored within is accurate, consistent, and conforms to predefined rules and relationships. They help maintain data integrity and prevent the introduction of errors or inconsistencies into the database.
Integrity constraints are rules or conditions that are used to maintain the accuracy, consistency, and validity of data in a database. They ensure that data entered into a database meets certain criteria, such as referential integrity, uniqueness, and data validity, which helps to maintain the integrity and reliability of the database.
Here are some commonly used integrity constraints:
1. Primary Key Constraint: This constraint ensures that each row in a table is uniquely identified by a primary key. It prevents duplicate or null values in the primary key column.
2. Foreign Key Constraint: This constraint establishes a relationship between two tables, where the foreign key in one table refers to the primary key in another table. It ensures that data entered into the foreign key column matches an existing value in the referenced table's primary key column.
3. Unique Constraint: This constraint ensures that values in a column or a combination of columns are unique and not duplicated within a table. It helps prevent duplicate entries.
4. Check Constraint: This constraint allows you to define certain conditions or expressions that must be satisfied for data entered into a column to be considered valid. It ensures that the data meets specific criteria.
5. Not Null Constraint: This constraint ensures that a column cannot have a null value. It enforces that a value must be provided for that column during data entry.
6. Domain Constraint: This constraint defines the allowable values for a column based on its data type. It restricts the range of values that can be entered.
By applying these integrity constraints, database designers can maintain the consistency, accuracy, and integrity of data, ultimately ensuring the reliability of the database.