Question

What is a primary key?

Short answer

Answer: A primary key is a unique identifier for a record in a database table, ensuring data integrity and establishing relationships between tables. It has several notable characteristics, such as uniqueness, non-nullability, immutability, and minimalism. Its primary purposes include maintaining data integrity, facilitating relationships through foreign keys, and enabling efficient querying through automatic indexing. Examples of primary keys include Student IDs, Order IDs, and Account Numbers.

Step-by-step solution

Primary Key Definition

A primary key is a unique identifier for a record in a database table. It cannot contain null values, and it must contain a unique value for each record in the table. The primary key is used to ensure data integrity and to establish relationships between tables in a database.

Primary Key Characteristics

The primary key has several important characteristics: 1. Uniqueness: Every record in the table must have a unique primary key value. 2. Non-nullable: The primary key cannot contain null values. 3. Immutable: The primary key value should not change once it is assigned to a record. 4. Minimal: The primary key value should be as small as possible and consist of the minimum number of attributes needed to uniquely identify a record.

Purpose of Primary Key

The primary key serves several purposes in a database: 1. Data Integrity: The primary key ensures that each record in a table is uniquely identified, preventing duplicates or data inconsistencies. 2. Relationships: Using primary keys, relationships can be created between tables (called foreign keys) to establish connections among data and create a relational database structure. 3. Efficient Querying: Primary keys are indexed automatically, which improves the query performance when searching for a specific record based on its primary key.

Examples of Primary Key

Examples of primary keys in a database might include: 1. Student ID for a table containing student information 2. Order ID for a table containing order details 3. Account Number for a table containing bank account information In general, primary keys can be any combination of alphanumeric characters, as long as they are unique for each record.