Google Data Analytics Professional Certification Practice Test

What does a primary key in a database do?

1. Connects two tables together

2. Indexes all data in a table

3. References a column with unique values

4. Contains duplicate entries

The correct answer is: References a column with unique values

A primary key in a database serves the critical function of uniquely identifying each record within a table. It ensures that no two rows can have the same value in that column, which helps maintain the integrity of the data. By enforcing this uniqueness, the primary key establishes a reliable system for retrieving and managing data, preventing any ambiguity that could arise from duplicate entries. This uniqueness is essential for efficiently organizing and accessing records, especially when performing operations such as searching, updating, or deleting data. Because a primary key must contain unique values, it inherently rules out the possibility of duplicate entries, thus not only serving as a unique identifier but also fulfilling a crucial role in the relational structure of databases. While connecting tables and indexing data are important concepts in database management, they pertain to different functionalities. A primary key doesn't directly connect tables; that role is typically fulfilled by foreign keys. Additionally, while indexing is important for improving data retrieval speed, it is not the core purpose of a primary key.