Lec-8: What is CANDIDATE KEY and PRIMARY key | Full Concept | Most suitable examples | DBMS

Summary

This script discusses the critical role of candidate keys in databases. It explains that a key is an attribute used to uniquely identify tuples in a table, preventing confusion between identical entries that could be duplicates or different entities. The candidate key set includes attributes like roll number, Aadhar card, license number, voter ID, and email ID, which are unique. From this set, one key is selected as the primary key, with the rest being alternative keys. The script emphasizes the importance of understanding how to design candidate keys and choose the primary key for database management.

Takeaways

• 🔑 A key in a database is an attribute that helps uniquely identify tuples in a table.
• 📚 The purpose of a key is to distinguish between rows that might appear to be the same.
• 👨‍🎓 Examples of keys include student ID, roll number, license number, voter ID, and phone number.
• 🚫 Duplicate values are not allowed for a key attribute to maintain uniqueness.
• 🤔 The database must be able to differentiate between coincidentally identical rows and intentionally duplicated rows.
• 🔍 Candidate keys are sets of attributes that can uniquely identify rows in a table.
• 🛠️ A primary key is chosen from the set of candidate keys and is used to uniquely identify each record.
• 🔄 Alternative keys are the remaining candidate keys after one is chosen as the primary key.
• 💼 Designing the correct set of candidate keys is crucial for effective database management.
• 🔑 The primary key is vital for the organization and integrity of the database.

Q & A

What is a key in the context of a database?

A key in a database is a normal attribute used to uniquely identify any two tuples (rows) in a table, ensuring that there is no confusion between rows with identical values.

Why is it important to have a key in a database?

Having a key in a database is crucial for distinguishing between rows that might appear to be the same, whether due to duplicate entries or coincidental identical data, thus maintaining data integrity.

What is a candidate key?

A candidate key is a set of attributes that can uniquely identify each row in a table without repetition. It is a potential key from which a primary key can be chosen.

How is a primary key selected from the candidate keys?

A primary key is chosen from the set of candidate keys, typically selecting the most appropriate one based on factors such as simplicity, uniqueness, and non-duplication of values.

What are some examples of attributes that can serve as candidate keys?

Examples of attributes that can serve as candidate keys include Aadhar card number, roll number, license number, voter ID, phone number, and email ID, as these attributes are unique and do not repeat within a table.

What is the role of a primary key in a database table?

A primary key plays a critical role in a database table by uniquely identifying each record and serving as the main index for data retrieval and manipulation.

Why is the selection of the primary key important in database design?

The selection of the primary key is important in database design because it affects the performance, integrity, and organization of the database. It should be chosen carefully to optimize these aspects.

What happens to the other candidate keys once a primary key is chosen?

Once a primary key is chosen, the remaining candidate keys are known as alternative keys. They can be used as unique identifiers in other contexts or for creating indexes to improve query performance.

Can a table have more than one primary key?

A table cannot have more than one primary key as it would lead to ambiguity in uniquely identifying rows. However, composite keys can be used if multiple columns are needed to ensure uniqueness.

How does the concept of a key relate to data duplication in a database?

The concept of a key helps prevent data duplication in a database by ensuring that each row can be uniquely identified, thus avoiding the accidental insertion of identical rows.

What is the significance of a key in ensuring data consistency?

A key is significant in ensuring data consistency as it helps maintain the accuracy and reliability of the data by ensuring that each piece of information is distinct and can be accurately referenced.