A self-join is used to join a table to itself, and here's why the selected answers are correct:
* Option B: It can be an outer join.A self-join can indeed be either an inner or an outer join, allowing for more flexibility in how records are matched and returned, especially useful in hierarchical or sequential data scenarios.
* Option E: The query must use two different aliases for the table.When performing a self-join, aliases are necessary to distinguish between the different instances of the same table in the query.
* Option F: The ON clause can be used.In SQL, the ON clause specifies the conditions that match rows in a self-join, offering a clear and structured way to define how the join works.
Other options are not universally true:
* Option A: It must be an inner join. Incorrect because, as explained, outer joins are also possible.
* Option C: The ON clause must be used. Incorrect because the WHERE clause might also be used to specify the join condition.
* Option D: It must be an equijoin. Incorrect because non-equijoins (like non-equality comparisons) can also be used in self-joins.