Which type of join is demonstrated by the following query? sql SELECT * FROM Make, Model WHERE Make.ModelID = Model.ID;

The query demonstrates an EQUIJOIN. An equijoin is a specific type of inner join that uses an equality operator (=) in the join condition to match rows from two or more tables based on common values. In this query, the WHERE Make.ModelID = Model.ID clause explicitly uses the equality operator to link the Make and Model tables. The syntax used is an older, implicit join notation, but the underlying operation is an equijoin because of the equality condition.

A. NON-EQUIJOIN: This is incorrect because a non-equijoin uses comparison operators other than equality (e.g., , BETWEEN), whereas this query uses =.

B. SELF JOIN: This is incorrect because a self join involves joining a table to itself. This query joins two different tables, Make and Model.

D. CROSS JOIN: This is incorrect because a cross join returns the Cartesian product of two tables (all possible row combinations). The WHERE clause filters the result, so it is not a full cross join.

1. Silberschatz, A., Korth, H. F., & Sudarshan, S. (2020). Database System Concepts (7th ed.). McGraw-Hill.

Section 4.3.2, "Join Conditions": The text explains, "A join operation in which the join condition consists only of equality comparisons... is called an equijoin." The provided query WHERE Make.ModelID = Model.ID fits this definition perfectly.

2. Oracle. (2023). Oracle Database SQL Language Reference, 23c.

Chapter 7, "Joins," Section "Equijoins": The documentation states, "An equijoin is a join with a join condition containing an equality operator. An equijoin combines rows that have the same values for the specified columns." This directly describes the operation in the question's WHERE clause.

3. Ullman, J. D., & Widom, J. (n.d.). CS145 Introduction to Databases, Lecture Notes. Stanford University.

SQL Joins Section: The course notes differentiate join types, defining an equijoin as a join where the condition is based on equality between values in the columns of the tables being joined. The example FROM R, S WHERE R.A = S.B is presented as the classic form of an equijoin.