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. A form of the WITH CLAUSE, “WITH RECURSIVE”, allows to design a recursive query: a query which repeats itself again and again, each time using the results of the previous iteration. This can be quite useful …