Get records with the newest date in Oracle - sql

Question

I need to find the emails of the last person that performed an action over a post. The database structure is a little bit complicated because of several reasons not important for the case.
SELECT u.address
FROM text t
JOIN post p ON (p.pid=t.pid)
JOIN node n ON (n.nid=p.nid)
JOIN user u ON (t.login=u.login)
WHERE n.nid='123456'
AND p.created IN (
SELECT max(p.created)
FROM text t
JOIN post p ON (p.pid=t.pid)
JOIN node n ON (n.nid=p.nid)
WHERE n.nid='123456');
I would like to know if there is a way to do use the max function or any other way to get the latest date without having to make a subquery (that is almost the same as the main query).
Thank you very much

Answer 1

You can use a window function (aka "analytical" function) to calculate the max date.
Then you can select all rows where the created date equals the max. date.
select address
from (
SELECT u.address,
p.created,
max(p.created) over () as max_date
FROM text t
JOIN post p ON (p.pid=t.pid)
JOIN node n ON (n.nid=p.nid)
JOIN user u ON (t.login=u.login)
WHERE n.nid='123456'
) t
where created = max_date;
The over() clause is empty as you didn't use a GROUP BY in your question. But if you need e.g. the max date per address then you could use
max(p.created) over (partition by t.adress) as max_date
The partition by works like a group by
You can also extend that query to work for more than one n.id. In that you you have to include it in the partition:
max(p.created) over (partition by n.id, ....) as max_date
Btw: if n.id is a numeric column you should not compare it to a string literal. '123456' is a string, 123456 is a number

Answer 2

SELECT address
FROM (
SELECT u.address,
row_number() OVER (PARTITION BY n.nid ORDER BY p.created DESC) AS rn
FROM text t JOIN post p ON (p.pid=t.pid)
JOIN node n ON (n.nid=p.nid)
JOIN user u ON (t.login=u.login)
WHERE n.nid='123456'
)
WHERE rn = 1;
The ROW_NUMBER function numbers the rows in descending order of p.created with PARTITION BY n.nid making separate partitions for row numbers of separate n.nids.