SQL-92 provides an n-ary operation called coalesce, which is defined as follows: coalesce (A1,A2, . . .

Question:

SQL-92 provides an n-ary operation called coalesce, which is defined as follows: coalesce (A1,A2, . . . , An) returns the first nonnull Ai in the list A1,A2, . . .,An, and returns null if all of A1,A2, . . .,An are null. Show how to express the coalesce operation using the case operation.