In every application development process, we often encounter scenarios where entities share common attributes while also possessing unique characteristics. We manage these parent-child-like relationships between entities using inheritance logic in our programs. Similarly, the PostgreSQL RDBMS provides a solution for addressing these cases through table inheritance. In this blog post, we will delve into the concept of table inheritance in PostgreSQL, discussing its advantages, disadvantages, and practical use cases.

Introduction & Definition

Table inheritance is a feature in PostgreSQL that allows you to create a hierarchy of tables based on a parent-child relationship. The child tables inherit the structure, constraints, and attributes of the parent table, while also having its definitions and additional attributes. This approach provides a convenient way to manage related data and simplify your database schema. To understand, let's see a simple and widely used scenario.

Suppose we have an application like HRMS or something wherein we have to manage employee data, and the organization has different types/categories of employees like full-time, part-time, contracts, special consultants etc. Each of these employees has some common attributes like first name, last name, email, joining date, date of birth etc but also specific attributes unique to those employee types. Below DDL script will help understand more,
Create the parent table called "employees" with common attributes:

-- Create the parent table called "employees" with common attributes:
CREATE TABLE employees (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100),
    hire_date DATE
);
-- Create child tables for each type of employee, inheriting from the "employees" table:

CREATE TABLE full_time_employees () INHERITS (employees);
CREATE TABLE part_time_employees () INHERITS (employees);
CREATE TABLE contractors () INHERITS (employees);

-- Add specific attributes to each child table:

-- Adding columns to the full-time employees table
ALTER TABLE full_time_employees ADD COLUMN salary NUMERIC(10, 2);
ALTER TABLE full_time_employees ADD COLUMN vacation_days INTEGER;

-- Adding columns to the part-time employees table
ALTER TABLE part_time_employees ADD COLUMN hourly_rate NUMERIC(10, 2);
ALTER TABLE part_time_employees ADD COLUMN hours_worked INTEGER;

-- Adding columns to the contractors table
ALTER TABLE contractors ADD COLUMN contract_rate NUMERIC(10, 2);
ALTER TABLE contractors ADD COLUMN contract_duration INTEGER;

In this example, the parent table "employees" contains common attributes shared by all employees. The child tables, such as "full_time_employees", "part_time_employees", and "contractors", inherit these common attributes and allow for the addition of specific attributes related to each employee type.

With the use of table inheritance, we have done,

• Maintained a centralized employee table for common attributes and shared functionality.

• For unique attributes of each employee type, we created separate child tables for types with those attributes, ensuring data integrity and clarity.

• Retrieval and Filtering of data while performing queries specific to each employee type using the child tables.

This approach provides flexibility in managing different types of employees while maintaining a consistent structure and enabling specific attributes for each employee type.

Similarly, it can be implemented for various product categories in an e-commerce database. Each product category has its unique attributes other than the common attributes. The parent table will be a product table having common attributes like product name, price, etc and child tables having attributes specific to each product type. This design can also be used in designing content management systems, where types of content are different.

Pros:

• Table inheritance allows you to organize your data with the parent table containing common attributes shared by all child tables, while each child table can have its specific attributes. This logical organization makes it easier to manage and query data.

• By centralizing common attributes in the parent table, you avoid duplicating columns across multiple tables.

• Constraints defined on the parent table are automatically enforced on all child tables. This ensures data integrity and consistency throughout the inheritance hierarchy.

• With table inheritance, you can perform queries on specific child tables to retrieve data relevant to a particular entity type. This allows for efficient filtering and retrieval of data based on specific attributes.

Cons:

• The query execution planner will have to consider the structure and constraints defined for both parent and child tables, in turn adding complexity to query planning and can result in slightly longer planning time.

• PostgreSQL uses indexes defined on the specific table, if any, for querying that table. This means that you may need to create separate indexes for each child table to optimize query performance.

• Table inheritance is often used for dividing or partitioning large tables into more manageable chunks, which is also known as data segmentation. But it introduces additional complexity in making complex execution plans and may involve querying multiple child tables, causing a performance drop.

• When performing maintenance operations like VACUUM or ANALYZE on a parent table, PostgreSQL will also process the child tables. This can increase the time required for these operations, especially if the inherited tables contain a significant amount of data.

Summary:

Table inheritance in PostgreSQL offers a robust method for organizing related data, enhancing code reusability, and preserving data integrity, which can streamline your database schema, minimize redundancy, and boost query adaptability. When devising your database, assess the entities, their shared attributes, and unique traits to establish if table inheritance is an appropriate strategy. Keep in mind the importance of meticulously designing your database schema and taking into account the particular requirements and access patterns of your application when employing table inheritance.