Database Foreign Key Constraints

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Questions and Answers

What does a foreign key in a database allow?

  • Duplicates and NULLs (correct)
  • Exclusively numeric values
  • Only unique values
  • Only multiple values

How many foreign keys can a table contain?

  • Only one
  • At least two
  • Up to three
  • Any number (correct)

What is another term used for the foreign key constraint?

  • Unique Key Constraint
  • Referential Integrity Constraint (correct)
  • Data Integrity Constraint
  • Primary Key Constraint

In the provided table structure, which column acts as a foreign key?

<p>Dept (A)</p> Signup and view all the answers

What role does 'DEPTID' serve in the 'DEPT' table?

<p>Primary Key (A)</p> Signup and view all the answers

Which of the following statements describes the relationship between the 'EMPLOYEE' and 'DEPT' tables?

<p>EMPLOYEE references DEPT through a foreign key. (B)</p> Signup and view all the answers

What does the term 'CHILD TABLE' refer to in the context of foreign keys?

<p>The table with the foreign key (D)</p> Signup and view all the answers

What is illustrated by the arrow in the table relationship diagram?

<p>Link between primary and foreign keys (A)</p> Signup and view all the answers

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Study Notes

Foreign Key Constraint

  • A foreign key in a database table, also known as a referential integrity constraint, acts as a link between two tables
  • It references a primary key in another table
  • Foreign keys can have duplicate values and be set to NULL (meaning no reference).
  • A single table can have multiple foreign keys.

Example Table Structure

  • The DEPT table contains the department ID (DEPTID) as the primary key and the department names (DNAME).
  • The EMPLOYEE table contains employee IDs (empld), employee names (Name) and a department field (Dept) acting as the foreign key.
  • The Dept column in EMPLOYEE references the DEPTID column in the DEPT table, ensuring that each employee is associated with a valid department.

Database Relationship

  • The diagram illustrates the relationship between two tables based on the foreign key constraint.
  • It shows a "CHILD TABLE" and "PARENT TABLE".
  • The "CHILD TABLE" (EMPLOYEE) contains the foreign key which references the primary key in the "PARENT TABLE" (DEPT).
  • The relationship is visualised with an arrow pointing from the CHILD TABLE to the PARENT TABLE.

Training Session

  • This document is likely part of a training session for database systems like MySQL.
  • The training material includes slides and diagrams.
  • The presentation includes specific sections focusing on the EMPLOYEE and DEPT tables as an example.

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