Question

I have a tables called pages, page_views, page_items and page_votes. The latter three tables contain a page_id foreign key in order to keep a record of each individual view, item and vote that belongs to a page.

When I query a page, I also want to retrieve COUNT page_views, COUNT page_items and SUM page_votes.vote.

I have pasted a query below. It retrieves the total number of views. I’ve made various attempts to add items and votes to it, but the result is either a syntax error or views/items/votes returned as an identical and ‘wrong’ number, probably due to the way I am joining.

How can I add items and votes to this query?

SELECT   Page.*,   COUNT(*) AS views FROM pages AS Page  INNER JOIN page_views AS PageView   ON Page.id = PageView.page_id  GROUP BY Page.id  ORDER BY views DESC    LIMIT 10 OFFSET 0 

Answer 1

This will select TOP 10 viewed pages, and will count items and votes only for these pages.

Efficient if you have lots of pages but need only 10 of them, eliminates unneeded counting.

SELECT  (         SELECT COUNT(*)         FROM   page_views         WHERE  page_views.page_id = pages.id         ) AS views_count,         (         SELECT COUNT(*)         FROM   page_items         WHERE  page_items.page_id = pages.id         ) AS items_count,         COALESCE(         (         SELECT SUM(vote)         FROM   page_votes         WHERE  page_votes.page_id = pages.id         ), 0) AS votes_sum FROM    pages ORDER BY         views_count DESC LIMIT 10 

Even more efficient query:

SELECT  pages.*,         (         SELECT COUNT(*)         FROM   page_items         WHERE  page_items.page_id = pages.id         ) AS items_count,         COALESCE(         (         SELECT SUM(vote)         FROM   page_votes         WHERE  page_votes.page_id = pages.id         ), 0) AS votes_sum FROM    (         SELECT  page_id, COUNT(*) AS cnt         FROM    page_views         GROUP BY                 page_id         ORDER BY cnt DESC         LIMIT 10         ) AS pvd,         pages WHERE  pages.id = pvd.page_id 

, eliminates unneeded joins with pages.