Use the recursion facility of SQL:1999 to express a so-called “same generation” query: Given a Parent relation, ?nd al l pairs of people who have the same ancestor and are removed from her by equal number of generations. (For example, a child is removed from her parent by one generation and from grandparent by two.)
What will be an ideal response?
CREATE RECURSIVE VIEW SameGeneration(Cousin1, Cousin2) AS
SELECT DISTINCT P.Parent, P.Parent
FROM Parent P
UNION
SELECT DISTINCT P.Child, P.Child
FROM Parent P
UNION
SELECT P1.Child, P2.Child
FROM Parent P1, Parent P2, SameGeneration S
WHERE P1.Parent = S.Cousin1 AND S.Cousin2 = P2.Parent
The ?rst two (non-recursive) queries create the initial pairs of the form p, p (certainly, two occurrences of the same person is removed from a common ancestor by the same number of generations). The last, recursive, subquery computes the rest.
Computer Science & Information Technology
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