Final answer:
A self-join is a concept in SQL where a table is joined to itself using standard JOIN operations such as INNER JOIN, OUTER JOIN, or CROSS JOIN. The term 'self join' is not an SQL keyword; it's the process of a table being joined to itself, requiring the use of table aliases.
Step-by-step explanation:
In answering your question, a self-join can only be specified in the FROM clause with the use of the JOIN keyword followed by the particular join type. These types include INNER JOIN, OUTER JOIN, and CROSS JOIN. Although the term 'self join' might imply a specific command, it does not actually refer to a keyword in SQL syntax. Instead, it describes a concept where a table is joined to itself. When performing a self-join, you must use table aliases to differentiate between the instances of the same table in the query.
So to answer your question correctly, none of the options presented explicitly include the term 'self join'. The correct usage involves picking either an INNER JOIN, OUTER JOIN, or CROSS JOIN, based on the specifics of the data retrieval task. A self-join is essentially a regular join, but it is used on the same table and requires aliases to prevent confusion between the columns in the SQL statement.