If both the main query and the subquery deal with the same table and the
subquery requires input parameters from the outer query, then we use an alias
of the table in the outer query.
Example 5.11.4 Let us find the student numbers of students whose advisor
is advising at least one other student. The information is contained in the
ADVISING table, and the following select construct uses both ADVISING (in
the subquery) and its alias A in the main query: