SQL provides an n-ary operation called coalesce, which is defined as
follows: coalesce(A1, A2, . . . , An) returns the first non null Ai in the list
A1, A2, . . . , An, and returns null if all of A1, A2, . . . , An are null.
Let a and b be relations with the schemas A(name, address, title), and
B(name, address, salary), respectively. Show how to express a natural full
outer join b using the full outer-join operation with an on condition and
the coalesce operation. Make sure that the result relation does not contain
two copies of the attributes name and address, and that the solution is correct
even if some tuples in a and b have null values for attributes name or address.
