In relational databases, it is possible to have more than one foreign key in a single table.

Question

BlackTom AI · Accepted Answer

Foreign keys enforce referential integrity by linking a column (or columns) in one table to the primary key of another table. Because referential links are per column (or set of columns), a single table can include many such links.

1) Relevant knowledge points and concepts
- Foreign key: a constraint making values in one table match primary key values in another table.  
- Referential integrity: ensures referenced rows exist (or actions are taken on delete/update).  
- Cardinality and relationship types: one child row can reference one parent row; a child table can reference multiple different parent tables or even the same parent table multiple times (self-reference).  
- Junction tables: common many-to-many implementations use two (or more) foreign keys in a single table.

2) Step-by-step reasoning
- A foreign key constraint applies to a column or set of columns, not to the table as a whole.  
- Nothing in relational theory prevents defining several such constraints in a single table.  
- Practical example: an Orders table commonly has customer_id and salesperson_id; both are foreign keys referencing Customers(id) and Employees(id). Both constraints coexist and are enforced independently.

3) Example SQL (intermediate steps / syntax)
CREATE TABLE Customers (id INT PRIMARY KEY, name VARCHAR(50));
CREATE TABLE Employees (id INT PRIMARY KEY, name VARCHAR(50));
CREATE TABLE Orders (
  id INT PRIMARY KEY,
  customer_id INT,
  salesperson_id INT,
  FOREIGN KEY (customer_id) REFERENCES Customers(id),
  FOREIGN KEY (salesperson_id) REFERENCES Employees(id)
);

4) Why the correct answer is correct
This demonstrates that a single table can have multiple foreign-key constraints, each referencing potentially different parent tables or the same table (self-join), fulfilling referential integrity for multiple relationships.

5) Why the other option (False) is incorrect
Claiming “False” would assert a table cannot have more than one foreign key; that contradicts relational database design norms, SQL implementations, and common patterns (e.g., junction tables and multi-parent relationships).

6) Conclusion
Therefore the correct answer is True, which matches the provided answer.

In relational databases, it is possible to have more than one foreign key in a single table.判断题

类似问题

Following are the definitions of 2 tables in a DBMS: EMPLOYEE(EmpID,FirstName,LastName,PositionID,Salary) POSITION(PositionID,PositionName,DeptID,EmplID) What is the foreign key in the Table EMPLOYEE?

Question 15

A table in a database can contain more than one foreign key.

In a relational database management system, what is a foreign key?

The attribute ClientID in the Orders table would be considered

Which of the following correctly describes a foreign key in the entity-relationship (ER) diagram?

If participation of EMPLOYEE in DEPARTMENT is optional, what is the typical implication for the DEPARTMENT_ID foreign key in EMPLOYEE?

All tables in relational databases must have a foreign key.

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