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Can a Foreign Key Reference Primary Keys from Two Separate Tables Simultaneously?

Linda Hamilton
Release: 2025-01-11 08:03:45
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Can a Foreign Key Reference Primary Keys from Two Separate Tables Simultaneously?

Foreign Key References Across Multiple Tables: A Structured Approach

This article addresses the challenge of creating a foreign key in a deductions table that references primary keys from both employees_ce and employees_sn tables within an "employees" database. Both employees_ce and employees_sn have unique primary keys. Is a direct dual foreign key reference possible?

The Efficient Solution: A Hierarchical Design

The optimal solution involves restructuring the database to reflect a hierarchical employee structure:

  1. Employee Hierarchy: View employees as a parent class with employees_ce and employees_sn as subclasses.

  2. Database Table Design: Create a three-table structure:

    • employees (id, name, ...): A central table holding common employee attributes. id is the primary key.
    • employees_ce (id, ce_specific_data, ...): Stores data specific to employees_ce. id is a foreign key referencing employees.id.
    • employees_sn (id, sn_specific_data, ...): Stores data specific to employees_sn. id is a foreign key referencing employees.id.
  3. Foreign Key Relationships: Establish foreign key constraints:

    • employees_ce.id references employees.id
    • employees_sn.id references employees.id
  4. Deductions Table: The deductions table will now have a single foreign key, employee_id, referencing the employees.id column.

This hierarchical model ensures referential integrity and efficiently manages data for different employee types. It avoids the complexities and potential inconsistencies of attempting a direct dual foreign key reference. The single foreign key in the deductions table provides a clear and unambiguous link to the relevant employee record.

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