Single Table Inheritance or Class Table Inheritance: Which is Better for Multi-User Type Databases?

Designing a Relational Database for Multiple User Types

When designing a relational database with multiple user types, it is essential to determine the best approach to model the data. This blog post explores two common options: Single Table Inheritance (STI) and Class Table Inheritance (CTI).

Single Table Inheritance (STI)

STI involves creating a single table for all user types. This table incorporates columns for data shared among all types, as well as a column to indicate the specific user type. Columns that do not apply to a particular user type are typically left null.

Advantages:

• Ease of querying: Combines all user data in a single table, simplifying queries.
• Reduces duplication: Eliminates the need for multiple tables with duplicate columns.

Disadvantages:

• Null values: Can introduce many null values in columns that do not apply to certain user types.
• Limited flexibility: Adding new user types or modifying existing ones requires altering the table structure.

Class Table Inheritance (CTI)

CTI employs a separate table for each user type. All common data is stored in a base "users" table, while data specific to each type is stored in its respective table. A foreign key in the subclass tables references the base "users" table.

Advantages:

• Flexible: Allows for easy addition of new user types and changes to existing types without altering the base table.
• Data integrity: Enforces relationships between user types through foreign keys.

Disadvantages:

• Requires multiple queries: Needs additional queries to retrieve all user-related data, as it is distributed across tables.
• Shared primary key: May introduce complexity in implementing shared primary keys between tables.

Other Considerations:

Other design options include using views to combine data from multiple tables or employing inheritance mechanisms in the database engine. However, these approaches may have limitations and require careful implementation.

Deciding between STI and CTI depends on the specific requirements and trade-offs involved. STI is suitable when user types share a significant amount of data and flexibility is not crucial. CTI is preferable when user types differ significantly and flexibility is essential. By carefully considering these design options, you can establish an efficient and scalable relational database for managing multiple user types.

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