Get another value from row with max value with group by clause - sql

Question

Sorry for the title. I have this table:
CREATE TABLE people
(
Id int IDENTITY(1,1) PRIMARY KEY,
name varchar(50) NOT NULL,
FatherId int REFERENCES people(Id),
MotherId int REFERENCES people(Id),
age int NOT NULL
);
Which you can populate with these commands:
insert into people (name, age) VALUES ('Jonny', 50 )
insert into people (name, age) VALUES ('Angela', 48 )
insert into people (name, age) VALUES ('Donny', 55 )
insert into people (name, age) VALUES ('Amy', 55 )
insert into people (name, FatherId, MotherId, age) VALUES ('Marcus', 1, 2, 10)
insert into people (name, FatherId, MotherId, age) VALUES ('Beevis', 1, 2, 5)
insert into people (name, FatherId, MotherId, age) VALUES ('Stew', 3, 4, 24)
insert into people (name, FatherId, MotherId, age) VALUES ('Emily', 3, 4, 25)
My Goal
I want to get the age and name of the oldest child of each set of parents.
Getting just the age was pretty simple:
SELECT MAX(age) FROM people WHERE FatherId IS NOT NULL GROUP BY FatherId
But what if I want to get the age and their corresponding name?
I have tried
select p1.name, p1.age
FROM people p1
INNER JOIN
(
SELECT FatherId, MAX(age) age
FROM people
GROUP BY FatherId
) p2
ON p1.FatherId = p2.FatherId
but this just gives all the children because of the FatherId matching.
I can't seem to get the primary key (Id) because of the GROUP BY clause.
I suppose if this is not possible then some table restructuring may be required to make it possible?
EDIT
Here is a solution I found using CROSS APPLY
select child.name, child.age
FROM people parents
CROSS APPLY
(
select top 1 age, name
from people child
where child.FatherId = parents.Id
ORDER BY age DESC
) child

Answer 1

Here's a simple tweak of your own attempt. One possible advantage of doing it this way it to allow for ties.
select p1.name, p1.age
from people p1 inner join
(
select FatherId, max(age) max_age
from people
group by FatherId
) p2
on p2.FatherId = p1.FatherId and p2.max_age = p1.age;
Also you did refer to "set of parents" in the question. To do that you'd need to group by and join on MotherId as well, assuming of course that this matches up with the real world where children commonly have only a single parent in common.

Answer 2

You can try this query and see this demo
select
name,age
from
(select p.*, rn=row_number() over(partition by p.fatherid,p.motherid order by age desc) from
people p join
(select fatherid,motherid from people
where coalesce(fatherid,motherid) is not null
group by fatherid,motherid)t
on p.fatherid=t.fatherid and p.motherid=t.motherid
)t where rn=1

Answer 3

Two nested sub-select statements can be combined with inner join :
SELECT p1.age, p2.name
FROM
(
SELECT max(age) age
FROM people
WHERE FatherId is not null
GROUP BY FatherId ) p1
INNER JOIN
(
SELECT age, name
FROM people
WHERE FatherId is not null ) p2
ON ( p1.age = p2.age );
age name
--- ------
10 Marcus
25 Emily
SQL Fiddle Demo

Answer 4

This will pick up both parents
declare #t TABLE
(
Id int IDENTITY(1,1) PRIMARY KEY,
name varchar(50) NOT NULL,
FatherId int,
MotherId int,
age int NOT NULL
);
insert into #t (name, age) VALUES
('Jonny', 50 ),
('Angela', 48 ),
('Donny', 55 ),
('Amy', 55 );
insert into #t (name, FatherId, MotherId, age) VALUES
('Marcus', 1, 2, 10),
('Beevis', 1, 2, 5),
('Stew', 3, 4, 24),
('Emily', 3, 4, 25);
select tt.name, tt.age
, tt.fatherName, tt.fatherAge
, tt.motherName, tt.motherAge
from (
select ta.*
, tf.name as fatherName, tf.age as fatherAge
, tm.name as motherName, tm.age as motherAge
, row_number() over (partition by ta.FatherID, ta.MotherID order by ta.age desc) as rn
from #t ta
left join #t tf
on tf.id = ta.fatherID
left join #t tm
on tm.id = ta.motherID
) as tt
where FatherID is not null
and rn = 1