Geographic Information Systems (GIS) Professional Certification Practice Exam

The correct choice refers to a foreign key as it is a field (or collection of fields) in one table that uniquely identifies a row of another table. This unique identifier establishes a relationship between the two tables, allowing data from one table to reference data in another. In relational databases, foreign keys are crucial for maintaining the integrity of relationships between tables, ensuring that each entry in one table corresponds to valid entries in another.

A primary key, on the other hand, is a unique identifier for a record within its own table and is used to distinguish unique records. A composite key involves the use of two or more fields in combination to create a unique identifier, whereas a unique key ensures that all values in a column are different from each other but does not inherently imply a relationship with another table. Understanding these distinctions helps clarify the role of foreign keys in relational databases, highlighting their importance in linking related data across different tables.