Understanding MySQL Primary Keys

What is a Primary Key?

• A Primary Key is a unique identifier for a record in a database table.
• It ensures that each record can be uniquely identified, which helps maintain data integrity.

Key Characteristics of a Primary Key

• Uniqueness: Each value in the primary key column must be unique.
• Non-null: A primary key cannot contain NULL values.
• Immutable: The values of primary keys should not change over time.

Purpose of a Primary Key

• It uniquely identifies each record in a table.
• It helps establish relationships between different tables in a database.

Creating a Primary Key

You can define a primary key when creating a table using the CREATE TABLE statement.

Example:

CREATE TABLE Employees (
    EmployeeID INT NOT NULL,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    PRIMARY KEY (EmployeeID)
);

Composite Primary Key

A Composite Primary Key consists of two or more columns that together form a unique identifier for a record.

Example:

CREATE TABLE OrderDetails (
    OrderID INT NOT NULL,
    ProductID INT NOT NULL,
    Quantity INT,
    PRIMARY KEY (OrderID, ProductID)
);

Benefits of Using Primary Keys

• Data Integrity: Ensures that no two records can have the same identifier.
• Efficient Data Retrieval: Improves query performance by allowing quicker searches.
• Relationship Management: Facilitates the creation of relationships between tables using foreign keys.

Conclusion

Primary keys are fundamental in database design for ensuring data integrity and efficient data management. Always choose primary keys wisely to reflect the uniqueness and stability of your data.