WGU Data Management - Foundations Exam - Topic 2 Question 12 Discussion

This query performs a join operation where records from the Make table and Model table are combined based on the condition Make.ModelID = Model.ID. This condition tests for equality, which is the definition of an EQUIJOIN.

Types of Joins in SQL:

EQUIJOIN (Correct Answer):

Uses an equality operator (=) to match rows between tables.

Equivalent to an INNER JOIN ON condition.

Example:

sql

SELECT *

FROM Employees

JOIN Departments ON Employees.DeptID = Departments.ID;

NON-EQUIJOIN (Incorrect):

Uses comparison operators other than = (e.g., <, >, BETWEEN).

Example:

sql

SELECT *

FROM Employees e

JOIN Salaries s ON e.Salary > s.MedianSalary;

SELF JOIN (Incorrect):

A table is joined with itself using table aliases.

Example:

sql

SELECT e1.Name, e2.Name AS Manager

FROM Employees e1

JOIN Employees e2 ON e1.ManagerID = e2.ID;

CROSS JOIN (Incorrect):

Produces Cartesian product (each row from Table A combines with every row from Table B).

Example:

sql

SELECT *

FROM Employees

CROSS JOIN Departments;

Thus, since our given query uses an equality condition (=) to join two tables, it is an EQUIJOIN.