Lec-9: What is Primary Key in DBMS | Primary Key with Examples in Hindi

Summary

This video from the Gate Smashers dives into the concept of primary keys in database management systems (DBMS). It explains the importance of keys in various exams and scenarios, including competitive exams and placements. The video uses the analogy of a lock and key to illustrate the uniqueness of primary keys in identifying database entries. It discusses candidate keys, their properties of being unique but potentially nullable, and contrasts them with primary keys, which are not only unique but also non-nullable and are assigned by the system. The video clarifies that a database can have only one primary key, emphasizing its critical role in ensuring data integrity and uniqueness.

Takeaways

• 🔑 The primary key in a database is a unique identifier for each record, ensuring that no two entries are the same.
• 📚 The concept of keys, including primary keys, is crucial in database management systems (DBMS) and is frequently tested in exams and interviews.
• 📝 Candidate keys are attributes that can uniquely identify a record, but they may allow for null values and are not necessarily unique across all records.
• 🚫 Primary keys must be unique and not null, meaning every record must have a value for the primary key, and no two records can share the same primary key value.
• 👨‍🎓 Examples of primary keys in educational settings include student registration numbers and roll numbers, which are assigned by the institution and cannot be chosen by the student.
• 🏢 In professional contexts, identifiers like passport numbers, Aadhaar card numbers, and license numbers serve as primary keys because they are issued by authorities and are both unique and mandatory.
• 🚫 It is not possible to have more than one primary key in a database because the primary key's role is to uniquely identify each record, and this cannot be achieved with multiple attributes.
• 🔍 The selection of a primary key depends on the context and the attributes available in the database, with factors like uniqueness and the necessity of having a value being key considerations.
• 🛠️ The primary key is a fundamental aspect of database normalization and is used to enforce data integrity and support relationships between tables.
• ❌ Attempting to assign a primary key that allows for null values or duplicates would lead to data anomalies and is not permitted in well-designed databases.

Q & A

What is the primary key in the context of a database?

The primary key is a unique identifier for each record in a database table, ensuring that each entry can be distinctly recognized and that no two records have the same key value.

Why is the concept of keys important in DBMS?

The concept of keys is crucial in DBMS because it helps in uniquely identifying records, ensuring data integrity, and is fundamental in database operations such as normalization and querying.

What is the difference between a primary key and a candidate key?

A candidate key is any column or set of columns that can uniquely identify a row in a table, while a primary key is the chosen candidate key that is used to uniquely identify each record in a table.

Can a table have more than one primary key?

No, a table cannot have more than one primary key because the primary key must uniquely identify each record, and having multiple would violate this uniqueness constraint.

What is the significance of the primary key being 'not null'?

The primary key being 'not null' ensures that every record in the database must have a value for the primary key, preventing the creation of records without an identifier.

Why is the primary key not chosen from user input?

The primary key is not chosen from user input because it needs to be unique and not null for every record. It is typically generated automatically by the system to maintain these constraints.

How does the concept of a primary key apply to real-world examples like student registration numbers or passport numbers?

In real-world examples, unique identifiers like student registration numbers or passport numbers serve as primary keys, ensuring that each individual's information is uniquely identifiable and distinct.

What happens if a candidate key is not unique or can be null?

If a candidate key is not unique or can be null, it cannot serve as a primary key because the primary key must guarantee both uniqueness and the presence of a value for every record.

Why are attributes like name, age, or date of birth not suitable as primary keys?

Attributes like name, age, or date of birth are not suitable as primary keys because they can have duplicate values, which violates the uniqueness requirement of a primary key.

How does the database ensure that the primary key remains unique and not null?

The database ensures the primary key remains unique and not null through constraints and system-generated values, preventing the insertion of duplicate or null values for the primary key.