If you have been using certain DBMSs, or reading recent versions
of the SQL standard, you are probably aware of the so-called
"WITH clause" of SQL.
Some call it Subquery Factoring. Others call it Common Table Expression.
In its simplest form, this feature is a kind of "boosted derived table".
Assume that a table T1 has three columns:
CREATE TABLE T1(
YEAR INT, # 2000, 2001, 2002 ... …