Assertion. Generally, a join query combines rows from multiple tables having some common column(s) and a joining condition, but not always.

Reason. A Cartesian product is an unrestricted join where all possible combinations of rows from multiple tables are created without any condition on them.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
In SQL, a join is a query that combines rows from two or more tables based on a specified condition, such as matching values in a common column. However, this matching condition is not always required; for instance, a Cartesian product is an unrestricted join where all possible combinations of rows from multiple tables are generated without any specific condition. This means that every row from one table is combined with every row from another table.