What Is Single Table Inheritance? Everything You Need to Know

Have you ever worked on any type of application like a blog, an e-commerce platform, or a SaaS product? If so, then you may easily understand how a database design is one of those things that start out easier and simpler at the beginning, but become difficult over time.

Initially, you only need to create a few tables, connect them through relationships, and things seem smooth. However, as your app starts to grow, things become more challenging. The app owners need to add new features, introduce multiple types of users, and most probably expand product categories. All of this certainly turns your clean database into a confusing web of joins and tables.

This is the point where design patterns like Single Table Inheritance, also known as STI, play their role. It is one of those concepts that can either be a developer’s favourite or an undeniable nightmare. Most developers love it for its simplicity, but struggle when it’s misused.

First-time users should know it can make applications faster and easier to manage if done correctly. But if something goes wrong, it can quickly become a major problem for a database.

Below, we have shared a detailed guide that offers a friendly explanation of single table inheritance.  We have discussed everything from its working to its benefits to help you understand whether it’s the right choice for your project or not.

Quick Summary

Single Table Inheritance (STI) can be defined as a way of organising data where different but related things are stored in a single place. They are not divided across multiple tables. It uses a simple label to help viewers understand the types of all data pieces. This approach is simpler and quicker at the start. But as the data and types increase, managing and organising can become complicated.

Key Takeaways:

• Single Table Inheritance organises the same type of data in a single table rather than using multiple tables.
• A simple “type” label is used to identify what is represented by each row.
• It helps to simplify the database design and speeds it up, especially during the initial stages.
• Because every piece of information is in a single place, fetching data becomes faster.
• Some fields can be left empty at times because they are not required for all data types.
• STI works wonders when multiple types share most of their details.
• It becomes complicated and difficult to manage when the system starts to expand and grow more complex.

What is Single Table Inheritance?

No matter the topic, it is always better to start with the basics. Whether you are looking to explore some essential web development tools for coding, or learning tips to help developers, organising information remains a requirement. Interestingly, Single Table Inheritance is a way of organising your database where you can store multiple related data types into a single table rather than splitting them across multiple tables. This process is performed using a special column usually labelled as 'type' that helps to identify what kind of data each row represents.

Imagine building a system responsible for managing different types of users.  These can include multiple types, like admins, vendors, and customers. When working as per a traditional approach, you can easily create separate tables for each type. However, by using single table inheritance, you can organise everything into a single table by labelling each row with its type.

This way, your table will have columns for all possible attributes across all user types, even in case some of these do not apply to every row. For instance, an admin might have a field named admin_level, whereas a retailer may have a field with the name store_name. Both columns exist in the same table, but only one is considered relevant according to its type.

Have a look at the table below.

For a beginner, this setting might feel a bit strange.  Viewers might wonder why to keep everything in a single place when you can easily organise it into separate tables. The answer mostly revolves around performance and simplicity; however, it comes with trade-offs as explained further.

How Single Table Inheritance Works?

Let us explain the working of STI through a simple and practical approach.

Step 1: One Table for All Entities

Rather than creating multiple tables for each type of data, one table is used to store all information. This way, users do not need to worry about managing multiple tables or finding ways to link them. All types of related data are stored in a single place, making the structure user-friendly.

Step 2: Add a Type Column

To organise things within a table, my special column, mostly labelled as type, is added. This column helps users to find the kind of record each row represents.  For instance, three different rows are marked as Admin, Customer, and Vendor. It is easy to clarify the difference by focusing on their types.

Step 3: Use Conditional Fields

This is the point where things become interesting for the user.  Since all types are stored within the same table, you will find columns for every possible field regardless of their compliance with a type.

Suppose the three types Admin, Customer, and Vendor will have columns with the names Admin_Level, Purchase_History, and Store_Name, respectively. Because every row does not require all of these fields, the ones that don’t comply will simply be left empty (NULL).

In a nutshell, every individual row will only use the fields that apply to its type, while the rest will remain empty or unused.

Why Developers Use Single Table Inheritance?

According to a report by a Stack Overflow Developer Survey, approximately 70% of developers prefer a simpler database schema when working on beginner-level applications.  It is because when you are working with closely related entities similar in most of their attributes, creating separate tables can be a difficult task.

Besides increasing complexity, it forces users to constantly deal with joins whenever they wish to fetch combined data. For this reason, using STI can change the game for developers. It lets you store your entire database in a single table, which makes it easier to understand, especially at the beginning.

Entrepreneurs working on startups or small projects can move faster, iterate quickly, and prevent getting confused with complex database structures. Another advantage of STI is in terms of performance. Because joins come with a particular price, having them used in large data sets can be expensive. Undoubtedly, STI keeps everything in a single table and eliminates the need for joins in most cases, hence leading to faster and more affordable queries.

Another report published by Oracle and PostgreSQL, reducing joins can enhance query execution by approximately 30 to 50% times in different scenarios. It is considered a significant boost, especially when focusing on read-heavy applications.

The Advantages of Single Table Inheritance

1.    Easy To Maintain

Of course, maintaining a single table is better than managing multiple tables. As a result, you find it easier to understand and modify your database schema.  This serves as a time-saving approach during development and debugging.

2.    Time-Savvy Queries

The next advantage is query performance. Because all of your data is stored in a single table, fetching records becomes easier. You can feel free from the hassle of joining multiple tables or maintaining relationships between them. This way, your application becomes faster and more responsive.

Example:

SQL:

SELECT * FROM users WHERE type = ‘Admin’;

3.    Beginner-Friendly Design

One of the most prominent advantages of single table inheritance is to get started. Rather than designing a complex schema with multiple relationships, you can easily create one table and build your app around it.  For this reason, it is an ideal choice for MVPs and early-stage products where speed is the first choice.

4.    Ideal for Similar Data Structures

Finally, the most important advantage of STI is its compliance with similar data structures.  If your entities have multiple common fields, splitting them into separate tables is not the right choice. Instead, it can make things unnecessarily complex. STI, in comparison, helps to maintain things efficiently and neatly in these cases.

The Disadvantages of Single Table Inheritance

1.    Too Many NULL Values

One of the biggest issues of single-table inheritance is having too many null values in the table. Because the table contains fields for all types of entity, plenty of rules will have unused fields. This can make your table look cluttered and difficult to understand.

2.    Difficult To Scale

Another disadvantage is scalability. While STI works smoothly for small to medium-sized applications, it can turn into a difficult choice when your system starts to grow. When all your data is held in a single table, it can expand on a larger level, which makes indexing and query optimisation challenging.

3.    Data Integrity Problems

The third disadvantage is data integrity. When working in a traditional multi-table setup, users can easily set up strict constraints for every table. In the case of single table inheritance, managing these constraints becomes very difficult because not all fields apply to all records.

Single Table Inheritance vs Other Approaches

Now let us compare STI with similar other approaches.

Comparison Table

Single Table Inheritance: When To Use and Avoid?

STI cannot be defined as a one-size-fits-all solution.

Best Use Cases

You can prefer using Single Table Inheritance when

• Most fields are common among entities.
• You are looking for fast read data.
• Your application is in the initial stages.
• There are fewer chances of frequently changing the data structure.

When Should You Avoid STIs?

Try to prevent using single table inheritance when,

• Entities have nothing in common.
• Plenty of optional fields exist in the table.
• There are higher chances of your system scaling massively.
• Data integrity is critical.

Best Practices for Using Single Table Inheritance

If you decide to use STI, follow these best practices.

1.    Limit the Number of Types

Always initiate through a simple design. By limiting the number of types, you can easily avoid unnecessary fields. Try not to make it complex, as you will find it difficult to manage later on.

2.    Utilise Clear Naming

Implement a consistent and clear naming for your type column. This way, users can easily understand what is represented by each record.

3.    Implement Proper Indexing

Try to add proper indexing to all the commonly queried fields. Have a look at the example below.

SQL:

CREATE INDEX idx_users_type ON users(type);

4.    Validate Data

Always pay attention to validation. Because the database is not efficient enough to enforce all constraints, you must have an application logic that makes sure data remains consistent.

5.    Analyse Table Growth

Make sure to monitor table growth regularly. Analyse the performance and try to refactor when required. It is not necessary to consider STI as a permanent solution. You can always try a new approach when your table starts to grow.

What to Consider Before Choosing Single Table Inheritance?

1.    Similarity in Entities

Start by checking the similarity between your entities. If most of their fields are common, STI can be a great fit. However, if the entities are entirely different, this strategy can be problematic in the future.

2.    Data Integrity Requirements

Make sure to consider whether your application relies heavily on complex updates for strict validation. In such cases, single table inheritance can bring plenty of limitations.

3.    Query Patterns

Another key factor to consider is the interaction of your app with the database.  If most of your queries are read-heavy and fetch similar types of data, STI can be the most suitable option.

4.    Chances of Scalability

Try to consider the scalability of your app. If you are planning to add plenty of new types and expand your data model, single table inheritance may not be considered the right long-term solution.

5.    Maintenance Complexity

Maintenance must also be considered for STI. It may be easier to manage in the beginning, but it becomes difficult to work with as the table expands.  Developers working on the project later can often find it confusing, especially if not all fields apply to every record.

Real-World Use Cases

Single table inheritance is an ideal choice in scenarios where your data is closely related and doesn't differentiate.

• A classic example is a user management system, where different types of users share most of their attributes.  Moreover, systems that manage different types of transactions and notifications can make the most of this approach.
• Another common example is product variants in e-commerce platforms.  If different types of products in your store share a primary set of attributes, storing them in a single table can help to simplify development and queries.

Common Mistakes Developers Must Avoid

• Avoid using STI for entities that are not similar.  This fills your table with relevant fields and makes management difficult.
• Do not apply STI without planning for growth. Often, developers choose this approach for its simplicity without calculating how the system will evolve.
• Do not ignore NULL values in single table inheritance. Because they are unavoidable, having plenty of them can prove that your design is not an ideal choice.
• Avoid using STIs without exploring other options.  Remember that it is just one of many approaches, rather than being the only right option.

Final Thoughts

In a nutshell, Single Table Inheritance seems like a simple concept.  However, it has a much stronger impact on the way your applications scale and perform.  If you pay attention to all the strengths and weaknesses of this approach, you can find it easy to make better decisions about your database design while preventing common pitfalls.

No matter if you’re building a small project or planning a large system, always understand the right way to use STI.  Implementing this approach properly can save you time and effort.

If you have completely understood everything about single table inheritance, make your decision. Now, you are in a much better position to know whether this approach is the right fit for your project or not.