What type of key serves as a unique identifier within a database table?

A primary key serves as a unique identifier within a database table, ensuring each record can be uniquely distinguished from all others. This key enforces the entity integrity of the database, meaning that no two rows can have the same key value, thereby preventing duplicate entries. A primary key is typically assigned to a single column but can also be a combination of multiple columns, ensuring uniqueness.

In database design, it's crucial to have a primary key so that relationships between tables can be established accurately; this is foundational in relational database management. When you establish relationships between tables, the primary key from one table acts as a reference point in another table as a foreign key, allowing for efficient data retrieval and maintaining the integrity of relational databases.