Understanding Primary Keys, Foreign Keys in RDBMS: Best Practices for Data Consistency and Integrity

Introduction to RDBMS: Understanding Primary Keys and Foreign Keys

Relational Database Management Systems (RDBMS) are designed to store data in tables with well-defined relationships between them. In this article, we’ll delve into the world of primary keys, foreign keys, and how they help maintain data consistency and integrity.

What are Primary Keys?

A primary key is a column or set of columns that uniquely identifies each row in a table. It’s used to identify individual records within a database and ensures data uniqueness across all rows.

In an RDBMS, primary keys are usually declared as the unique identifier for each record, which helps maintain data consistency and reduces errors during data insertion, updating, and deletion.

What are Foreign Keys?

A foreign key is a column or set of columns in one table that references the primary key of another table. This establishes relationships between tables and ensures referential integrity, meaning that if you try to delete or update data in the referenced table, the referencing table won’t allow it unless there are no dependencies.

In our scenario, we have two tables: Screenplay and Scene. The Screenplay table has a primary key (Scrn_ID) that uniquely identifies each screenplay, while the Scene table has a foreign key (Scene_Id) that references this Scrn_ID. This establishes a relationship between screenplays and their associated scenes.

Generating a Locally Unique Key for a Relational Table with Foreign Key

Now, let’s get back to the question at hand: How should we generate a locally unique key for the Scene table?

The Obvious Choice: Auto-Increment Integer Field Type

The first instinct might be to use an auto-increment integer field type for scene_id. This is indeed a simple and efficient solution:

CREATE TABLE Scene (
    scene_id BIGINT PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
    scene_name VARCHAR(255),
    Scrn_ID INT,
    FOREIGN KEY (Scrn_ID) REFERENCES Screenplay(Scrn_ID)
);

In this example, the scene_id column is declared as a big integer type with primary key constraint. The GENERATED ALWAYS AS IDENTITY clause automatically assigns a unique identifier to each new row inserted into the table.

But Is This Really Necessary?

At first glance, it might seem unnecessary to create a globally unique key for each scene when we’re dealing with screenplays and scenes within those screenplays. However, there are several reasons why this approach makes sense:

Data Consistency: Even if we only need a locally unique key, ensuring data consistency is crucial for maintaining accurate records.
Easier Data Retrieval: With an auto-incrementing primary key, it’s easier to retrieve all scenes associated with a particular screenplay or all screenplays featuring a specific scene.

While there might be situations where overkill seems like the right choice (like when dealing with very large datasets), using an auto-incrementing integer field type for scene_id is indeed a simple and efficient solution in our case, given that we’re only dealing with relatively small datasets.

Why Not Use Relative Numbers?

Some question on Stack Overflow suggest alternative solutions where relative numbers are used instead of globally unique keys:

CREATE TABLE Scene (
    scene_id INT,
    scene_name VARCHAR(255),
    Scrn_ID INT,
    FOREIGN KEY (Scrn_ID) REFERENCES Screenplay(Scrn_ID)
);

-- Inserting new row:
INSERT INTO Scene (scene_id, scene_name, Scrn_ID) 
VALUES ((SELECT MAX(Scrn_ID) FROM Screenplay), 'Scene Description', 1001);

In this scenario, the relative numbers are chosen based on the last Scrn_ID used for a specific screenplay. This approach can be seen as more “intelligent” because it takes into account previous data when determining new scene IDs.

However, these approaches have their own set of drawbacks:

Higher Overhead: With an alternative solution that relies on relative numbers, we need to ensure consistency by choosing the right number, which adds overhead in terms of complexity and potential errors.
Expensive to Implement: Such alternatives often require additional infrastructure or custom logic to manage relative numbers accurately. This can be expensive to implement compared to a straightforward auto-incrementing solution.

Why Keeping it Simple is Preferable

In conclusion, while alternative solutions exist for generating locally unique keys for the Scene table, using an auto-incrementing integer field type remains the simplest and most efficient solution in our case:

CREATE TABLE Scene (
    scene_id BIGINT PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
    scene_name VARCHAR(255),
    Scrn_ID INT,
    FOREIGN KEY (Scrn_ID) REFERENCES Screenplay(Scrn_ID)
);

This straightforward approach reduces complexity, ensures data consistency and integrity, and provides an easy-to-implement solution for managing locally unique keys.

Best Practices

In general, when working with RDBMS, keep in mind the following best practices:

Use primary keys (auto-incrementing or manually assigned) to uniquely identify each record.
Establish relationships between tables using foreign keys.
Ensure referential integrity by specifying constraints on your database schema.

By adhering to these guidelines and choosing the right approach for your specific use case, you can ensure robust, reliable, and maintainable databases that scale well with growing data sets.

Last modified on 2023-06-07