SQL query to retrieve families with only one generation from a family db

Question

Hi,
I need to write an SQL query that would select families with only one generation ((which means a person - or a married couple - with kids) or (a person - or a married couple - with parents but no kids)) from a database containing families. The simplified db structure is:
person:
id - int, primary key
siblings:
id
parent_id
kid_id
marriage
id:
husband_id
wife_id
Could anyone please help me? I dont really have any idea how to accomplish that...

Answer 1

Hi,
Welcome to the forum!
Assuming that siblings (despite its name) contains only parent-child relationships, and that the parent_id could be either the mother or the father:
WITH     got_tree     AS
     SELECT     CONNECT_BY_ROOT  s.parent_id     AS root_id
     ,     LEVEL                     AS lvl
     FROM          siblings     s
     LEFT OUTER JOIN     marriage     m     ON     s.parent_id     IN ( m.husband_id
                                                        , m.wife_id
     START WITH     parent_id     NOT IN     (  SELECT  kid_id
                                           FROM        siblings
     CONNECT BY     s.parent_id     IN ( PRIOR m.husband_id
                            , PRIOR m.wife_id
                            , PRIOR kid_id
SELECT       root_id
FROM       got_tree
GROUP BY  root_id
HAVING       MAX (lvl)     <= 2
;This will get a list of parents who may or may not have children, but who do not have either parents or grandchildren.
To get their spouses and children (if any) you will have to join this result set to all the other tables. At that point, you can eliminate poeple who do not have ancestors themselves, but are married to people who have more than one generation of ancestors.
The details of how to do that depend on the details of your tables. If you'd like help, then post a little sample data (CREATE TABLE and INSERT statements for all tables) and the results you want from that data.
Edited by: Frank Kulash on Oct 14, 2009 4:05 PM
I'd need sample data in order to test this, of course.