Is Primary Key Unique by Default?

Answer: Yes, a primary key is unique by default.

The primary key serves as a unique identifier for each record within a table, ensuring that no two records have the same key value.

Characteristics of Primary Key

• Identifies Individual Records: A primary key acts as a unique fingerprint for each row, allowing efficient retrieval and modification of specific data points.
• Enforces Data Integrity: By preventing duplicates, primary keys eliminate confusion and inconsistencies, ensuring data accuracy and reliability.
• Optimizes Queries and Joins: Unique primary keys enable faster search and join operations, improving database performance and scalability.
• No Null Values: Primary keys cannot contain null values, further guaranteeing their uniqueness and completeness.
• Single or Composite: A primary key can be a single column or a combination of multiple columns for complex identification needs.
• Uniqueness Constraints: Many database systems enforce uniqueness through explicit constraints, but even without them, duplicates within a primary key are automatically rejected.

Conclusion

The primary key is unique by default. The uniqueness of the primary key is a crucial aspect of relational database design, providing a reliable means of uniquely identifying and accessing individual records within a table.