Count / sum values in subquery and order by it

Question

I have tables like below:

user
    id | status
    1  | 0

gallery 
    id | status | create_by_user_id 
    1  | 0      | 1
    2  | 0      | 1
    3  | 0      | 1

media      
    id | status
    1  | 0
    2  | 0
    3  | 0

gallery_media      
         fk gallery.id fk media.id
    id | gallery_id | media_id | sequence
    1  | 1          | 1        | 1
    2  | 2          | 2        | 1
    3  | 2          | 3        | 2

monitor_traffic
                                  1:gallery 2:media
    id | anonymous_id | user_id | endpoint_code | endpoint_id
    1  | 1            |         | 1             | 2      gallery.id 2
    2  | 2            |         | 1             | 2      gallery.id 2
    3  |              | 1       | 2             | 3      media.id 3 include in gallery.id 2
    these means gallery.id 2 contain 3 rows 

gallery_information
         fk gallery.id    
    id | gallery_id

gallery includes media.

monitor_traffic.endpoint_code: 1 .. gallery; 2 .. media
If 1 then monitor_traffic.endpoint_id references gallery.id

monitor_traffic.user_id, monitor_traffic.anonymous_id integer or null

Objective

I want to output gallery rows sort by count each gallery rows in monitor_traffic, then count the gallery related media rows in monitor_traffic. Finally sum them.

The query I provide only counts media in monitor_traffic without summing them and also does not count gallery in monitor_traffic.

How to do this?

This is part of a function, input option then output build query, something like this. I hope to find a solution (maybe with a subquery) that does not require to change other parts of the query.

Query:

SELECT
  g.*,
  row_to_json(gi.*) as gallery_information
  FROM gallery g 
  LEFT JOIN gallery_information gi ON gi.gallery_id = g.id
  LEFT JOIN "user" u ON u.id = g.create_by_user_id
  -- start    
  LEFT JOIN gallery_media gm ON gm.gallery_id = g.id
  LEFT JOIN (
    SELECT 
      endpoint_id, 
      COUNT(*) as mt_count
      FROM monitor_traffic
      WHERE endpoint_code = 2
      GROUP BY endpoint_id
  ) mt ON mt.endpoint_id = m.id
  -- end
ORDER BY mt.mt_count desc NULLS LAST;

sql fiddle

score 1 · Accepted Answer · edited May 23 '17 at 12:07

I suggest a CTE to count both types in one aggregation and join to it two times in the FROM clause:

WITH mt AS (  -- count once for both media and gallery
   SELECT endpoint_code, endpoint_id, count(*) AS ct
   FROM   monitor_traffic
   GROUP  BY 1, 2
   )
SELECT g.*, row_to_json(gi.*) AS gallery_information
FROM   gallery g
LEFT   JOIN mt ON mt.endpoint_id = g.id  -- 1st join to mt
              AND mt.endpoint_code = 1   -- gallery
LEFT   JOIN (
   SELECT gm.gallery_id, sum(ct) AS ct
   FROM   gallery_media gm 
   JOIN   mt ON mt.endpoint_id = gm.media_id  -- 2nd join to mt
            AND mt.endpoint_code = 2          -- media
   GROUP  BY 1
   ) mmt ON mmt.gallery_id = g.id
LEFT   JOIN gallery_information gi ON gi.gallery_id = g.id
ORDER  BY mt.ct DESC NULLS LAST   -- count of galleries
       , mmt.ct DESC NULLS LAST;  -- count of "gallery related media"

Or, to order by the sum of both counts:

...
ORDER  BY COALESCE(mt.ct, 0) + COALESCE(mmt.ct, 0) DESC;

Aggregate first, then join. That prevents complications with "proxy-cross joins" that multiply rows:

Two SQL LEFT JOINS produce incorrect result

The LEFT JOIN to "user" seems to be dead freight. Remove it:
~~LEFT JOIN "user" u ON u.id = g.create_by_user_id~~

Don't use reserved words like "user" as identifier, even if that's allowed as long as you double-quote. Very error-prone.

Thanks for reply, I try this now (the left join user is because there's option if want to select where status = .. `gallery.status` `media.status` `media.create_by_user_id` > `user.status` ) — user1575921, May 01 '16 at 04:20
@user1575921: In this case, just add it back. It's orthogonal to the question. — Erwin Brandstetter, May 01 '16 at 04:24

Count / sum values in subquery and order by it

Objective

1 Answers1