Year 11 Exam > Year 11 Notes > IGCSE Information and Communication Technology Preparation > Primary & Foreign Keys
Primary & Foreign Keys | IGCSE Information and Communication Technology Preparation - Year 11 PDF Download
What is a Primary Key?
- Each table includes a primary key field serving as a unique identifier.
- Every piece of data in this field is distinct, preventing duplicate entries.
- This ensures that duplicate data is blocked from being entered into the primary key field, maintaining data integrity.
- The unique nature of data within the primary key field allows for the identification of individual records.
- In a database table like the one for customers, the primary key is crucial. It uniquely identifies each customer, making sure that even if there are customers with the same name, they can be differentiated correctly using the CustomerID.
- The CustomerID serves as the primary key because each customer's ID is unique.
Creating and Editing Keys
- Primary key: This key ensures each record in a table is uniquely identified.
- Foreign key: Used to establish relationships between tables by linking them together. The foreign key in one table matches the primary key in another.
Creating Relationships Between Tables
- Relational databases enable the establishment of relationships among various tables through primary and foreign keys.
What is a Foreign Key?
- A foreign key is a way to link tables together using primary keys.
- When we have a table with customer details, we can include another table displaying the subscriptions that customers possess.
- For instance, in the given scenario, CustomerID acts as a foreign key since it establishes a link with the CustomerID in the customer table mentioned previously.
Question for Primary & Foreign KeysTry yourself: What is the purpose of a primary key in a database table?View Solution
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FAQs on Primary & Foreign Keys - IGCSE Information and Communication Technology Preparation - Year 11
| 1. What is a Primary Key? |  |
Ans. A Primary Key is a unique identifier for each record in a database table. It ensures that each record can be uniquely identified and helps in maintaining data integrity.
| 2. How is a Primary Key different from a Foreign Key? | |
Ans. A Primary Key uniquely identifies each record in a table, while a Foreign Key establishes a relationship between two tables based on a key from one table matching a key in another table.
| 3. Why is it important to have a Primary Key in a database table? | |
Ans. Having a Primary Key in a database table ensures data integrity by preventing duplicate records and helps in efficiently retrieving and updating specific records in the table.
| 4. Can a Primary Key be NULL? | |
Ans. In most database systems, a Primary Key cannot be NULL as it needs to uniquely identify each record. However, there are exceptions in some systems where a NULL Primary Key is allowed.
| 5. How can you define a Primary Key in a database table? | |
Ans. A Primary Key can be defined when creating a table by specifying a column as the Primary Key or by altering an existing table to add a Primary Key constraint to a column.
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Dec 22, 2024 Last updated |
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