What is a Cartesian join in SQL?

• A. A join on matching keys
• B. A join between two unrelated tables
• C. A join that creates a combination of every row from both tables
• D. A join that requires a WHERE clause

Answer: (C)

A Cartesian join, also known as a cross join, produces a result set that contains every possible combination of rows from two tables. When two tables are involved in a Cartesian join, the total number of rows in the output is the product of the number of rows in the first table and the number of rows in the second table. This means if the first table has 3 rows and the second has 4, the result will consist of 12 rows (3 multiplied by 4).

The other options describe joins incorrectly or specify conditions that do not apply to Cartesian joins. For instance, a join on matching keys typically refers to inner joins where rows are combined based on related fields. The concept of unrelated tables might imply a misunderstanding of how data relationships work in SQL, as Cartesian joins do not require a relationship—they simply produce a combination of all rows. While it is possible to add a WHERE clause to filter the results of a Cartesian join, it is not necessary for the join itself to function, which distinguishes it from other join types that primarily rely on such conditions for meaningful results.