Which type of key is unique for each record in a table?

The primary key is the type of key that is unique for each record in a table. It serves as a unique identifier for the table's rows, ensuring that no two records can have the same primary key value. This uniqueness is fundamental for maintaining the integrity of the database, as it allows for efficient retrieval, updating, and management of the data.

In a relational database, the primary key is typically defined as one or more columns that contain values which do not repeat – thus providing a distinctive reference for each entry. This prevents duplicate rows and establishes a reliable way to track each record.

The other types of keys, while important in their own contexts, do not fulfill the same role of providing a unique identifier for a record within a table. For instance, surrogate keys represent a unique identifier generated by the database system, foreign keys create relationships between tables by referencing primary keys, and composite keys are a combination of two or more columns to create a unique identifier for a record, which may be necessary in certain scenarios but do not serve as the primary key alone.