How to find parent's youngest child's name
Solution 1:
You can use ROW_NUMBER() function to number records.
This numbering is based on motherId,fatherId which is sorted by age column.
After that, you can extract the numbers 1 of each family.
Use this:
select id,motherId,fatherId,name,age from
(select *
,DENSE_RANK() over (partition by motherId,fatherId order by age asc ) as rn
from people where (motherId is not null and fatherId is not null ))u
where u.rn=1
Result:
id motherId fatherId name age
4 2 1 Seth 20