Single Table Inheritance or Class Table Inheritance: Which is Right for Your Multi-User Database?

Relational Database Design for Multiple User Types

When designing a relational database that accommodates multiple user types, it's crucial to consider the efficient storage and retrieval of user data. The two main approaches for handling this scenario are:

Single Table Inheritance (STI)

STI involves creating a single table for all user types, with a "discriminator" column that indicates the specific type of each row. Columns that are not applicable to a particular user type are left NULL.

Advantages:

• Simple and straightforward to query for all user data in one go.
• Reduces data redundancy.

Disadvantages:

• NULL values in non-applicable columns can lead to data complexity and increase the storage size.

Class Table Inheritance (CTI)

CTI, unlike STI, uses a separate table for each user type. A common "users" table holds the shared information, while the type-specific tables contain the subclass-dependent data. The subclass tables typically reference the matching row in the "users" table using a foreign key.

Advantages:

• Allows for more tailored data structures for each user type.
• Eliminates NULL values in the subclass tables.
• Enforces referential integrity.

Shared Primary Key Design (SPK)

A variation of CTI, SPK involves setting the primary key of the subclass tables to be a copy of the primary key from the corresponding row in the "users" table. This technique ensures both a primary key and a foreign key relationship between the tables.

Advantages:

• Maintains a one-to-one relationship between users and subclasses.
• Improves query performance by speeding up joins.

The choice between STI and CTI depends on the specific requirements of the application. STI is suitable when the different user types have similar data structures and when there is a need for efficient data retrieval across types. CTI is preferable when the data structures vary significantly and when referential integrity and tailored storage are important. SPK enhances CTI by improving performance and enforcing the one-to-one relationship.

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