Postgres - order by aggregate function on SUM - sql

Question

I use Postgres sql function it in my sql query like:
SELECT
message.id,
note,
earned_media_direct(
SUM(message_stat.posts_delivered)::int,
CAST(SUM(message_stat.clicks) AS bigint),
team.earned_media_multi_clicks::int,
SUM(message_stat.likes)::int,
team.earned_media_multi_likes::int,
SUM(message_stat.comments)::int,
team.earned_media_multi_comments::int,
SUM(message_stat.shares)::int,
team.earned_media_multi_shares::int
) AS media_points,
count(*) OVER() AS total_count
FROM message
LEFT JOIN team ON team.id = 10
WHERE team_id = 10
GROUP BY message.id, team.id
{$orderBy}
LIMIT 20 OFFSET 1
When returning a list of messages I want to use ORDER BY rank (Sorting by "rank" really means sorting by Media Points)
The function earned_media_direct is defined within Postgres like:
CREATE OR REPLACE FUNCTION public.earned_media_direct(posts bigint, clicks bigint, clicks_multiplier numeric, likes bigint, likes_multiplier numeric, comments bigint, comments_multiplier numeric, reshares bigint, shares_multiplier numeric)
RETURNS numeric
LANGUAGE plpgsql
AS $function$
BEGIN
RETURN COALESCE(clicks, 0) * clicks_multiplier +
COALESCE(likes, 0) * likes_multiplier +
COALESCE(comments, 0) * comments_multiplier +
(COALESCE(posts, 0) + COALESCE(reshares, 0)) * shares_multiplier;
END;
$function$
I tried adding:
ROW_NUMBER() OVER (
ORDER BY earned_media_direct(
SUM(message_stat.posts_delivered),
CAST(SUM(message_stat.clicks) AS bigint),
team.earned_media_multi_clicks,
SUM(message_stat.likes),
team.earned_media_multi_likes,
SUM(message_stat.comments),
team.earned_media_multi_comments,
SUM(message_stat.shares),
team.earned_media_multi_shares) DESC
) AS rank
I am not sure I am using it right regarding my example. Is there another way to perform ORDER BY rank.
Thanks

Answer 1

We probably can use "subquery" approach for this
First: we wrap your main query into subquery and omit the order inside
it.
Second: we do order on outer query.
-- outer query
SELECT * FROM (
-- sub query (your main query)
SELECT
message.id,
note,
earned_media_direct(
SUM(message_stat.posts_delivered)::int,
CAST(SUM(message_stat.clicks) AS bigint),
team.earned_media_multi_clicks::int,
SUM(message_stat.likes)::int,
team.earned_media_multi_likes::int,
SUM(message_stat.comments)::int,
team.earned_media_multi_comments::int,
SUM(message_stat.shares)::int,
team.earned_media_multi_shares::int
) AS media_points,
count(*) OVER() AS total_count
FROM message
LEFT JOIN team ON team.id = 10
WHERE team_id = 10
GROUP BY message.id, team.id
LIMIT 20 OFFSET 1
) A
-- move the order to outer query
ORDER BY A.media_points;
Hope this help answer your question.
Reference:
https://www.postgresql.org/docs/current/functions-subquery.htm