Relational databases ensure data integrity through several mechanisms, including data types, primary keys, foreign keys, and constraints. These features work together to maintain accurate and consistent data within the database. By defining specific data types for each column, a database can enforce rules that prevent incorrect data entry. For example, if a column is designated for integers, trying to insert a string value will trigger an error, ensuring that only valid data is accepted.
Primary keys are another key aspect of data integrity. A primary key uniquely identifies each record in a table, ensuring that there are no duplicate entries. For example, in a customer database, using an email address or a customer ID as a primary key ensures that each customer record is unique and easily retrievable. This not only helps with avoiding redundancy but also fortifies the integrity of relationships in the data model. Furthermore, when a primary key is defined, the database automatically enforces the uniqueness of this key, preventing any attempts to insert a duplicate.
Foreign keys enhance data integrity by establishing relationships between tables. A foreign key in one table refers to the primary key of another table, ensuring that there are valid links between related records. For instance, if a database has a table for orders that references a customer table, a foreign key constraint will ensure that each order is associated with an existing customer. This prevents orphan records, which are entries that reference a non-existing record in another table. In combination, these mechanisms help maintain the accuracy and reliability of data across the entire database system, promoting overall data integrity.