Final answer:
In a relational database, a primary key uniquely identifies each row and is unique and not null, distinguishing it from other database components and allowing it to enforce data integrity through relationships.
Step-by-step explanation:
In a relational database, a primary key serves a special purpose compared to other components. The primary key of a table is a column or a set of columns that uniquely identifies each row in the table. No two rows can have the same primary key value, which ensures that each record can be distinctively identified. This is in contrast to other columns that may contain duplicate values or even nulls. Furthermore, the primary key is often used to establish and enforce relationships between tables in a relational database where it can be referenced as a foreign key in another table. This referencing supports the integrity of data by maintaining consistent and synchronized data across multiple tables.