How to Design a Relational Database for Multiple User Types: Shared Primary Key vs. Other Approaches?

Relational Database Design for Multiple User Types

In designing a relational database, it often becomes necessary to cater to multiple types of users who possess both unique and shared data attributes. Several approaches exist for addressing this aspect, each presenting its own advantages and drawbacks.

Option 1: Main User Table with User Type Column

This approach involves creating a central user table containing common information such as username, password, and a user_type column. Querying specific user data requires selecting their user type and subsequently executing individual queries for each type. This method suffers from the need for multiple queries and potential data duplication.

Option 2: User Type Tables with Foreign Keys

An alternative approach is to forgo the user_type column in the main user table and employ foreign keys linking user type-specific tables to the main users table. This eliminates redundant data but necessitates multiple queries equal to the number of user types when fetching data.

Option 3: Single Table Inheritance

In this design, a single table accommodates all user types. Columns that do not apply to a specific row are left null. An additional user_type column is used to differentiate between types. This approach simplifies queries but may result in sparse tables with many null values.

Option 4: Class Table Inheritance (with Shared Primary Key)

Similar to Option 2, there is a main user table containing common data. For each user type, a corresponding table exists with type-specific attributes. A shared primary key ensures that the key field in the user type table also acts as a foreign key referencing the main user table. This method enforces the one-to-one relationship and optimizes join performance.

The choice of approach ultimately depends on the specific requirements of the system. However, the shared primary key technique offers a balance between data integrity, efficiency, and flexibility, making it a preferred option in many scenarios.

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