Question

So I decided to try out PostgreSQL instead of MySQL but I am having some slight conversion problems. This was a query of mine that samples data from four tables and spit them out all in on result.

I am at a loss of how to convey this in PostgreSQL and specifically in Django but I am leaving that for another quesiton so bonus points if you can Django-fy it but no worries if you just pure SQL it.

SELECT links.id, links.created, links.url, links.title, user.username, category.title, SUM(votes.karma_delta) AS karma, SUM(IF(votes.user_id = 1, votes.karma_delta, 0)) AS user_vote
FROM links
LEFT OUTER JOIN `users` `user` ON (`links`.`user_id`=`user`.`id`)
LEFT OUTER JOIN `categories` `category` ON (`links`.`category_id`=`category`.`id`) 
LEFT OUTER JOIN `votes` `votes` ON (`votes`.`link_id`=`links`.`id`)
WHERE (links.id = votes.link_id)
GROUP BY votes.link_id
ORDER BY (SUM(votes.karma_delta) - 1) / POW((TIMESTAMPDIFF(HOUR, links.created, NOW()) + 2), 1.5) DESC
LIMIT 20

The IF in the select was where my first troubles began. Seems it’s an IF true/false THEN stuff ELSE other stuff END IF yet I can’t get the syntax right. I tried to use Navicat’s SQL builder but it constantly wanted me to place everything I had selected into the GROUP BY and that I think it all kinds of wrong.

What I am looking for in summary is to make this MySQL query work in PostreSQL. Thank you.

Current Progress

Just want to thank everybody for their help. This is what I have so far:

SELECT links_link.id, links_link.created, links_link.url, links_link.title, links_category.title, SUM(links_vote.karma_delta) AS karma, SUM(CASE WHEN links_vote.user_id = 1 THEN links_vote.karma_delta ELSE 0 END) AS user_vote
FROM links_link
LEFT OUTER JOIN auth_user ON (links_link.user_id = auth_user.id)
LEFT OUTER JOIN links_category ON (links_link.category_id = links_category.id) 
LEFT OUTER JOIN links_vote ON (links_vote.link_id = links_link.id)
WHERE (links_link.id = links_vote.link_id)
GROUP BY links_link.id, links_link.created, links_link.url, links_link.title, links_category.title
ORDER BY links_link.created DESC
LIMIT 20

I had to make some table name changes and I am still working on my ORDER BY so till then we’re just gonna cop out. Thanks again!

Answer 1

A few things:

1. Drop the backticks
2. Use a CASE statement instead of IF() CASE WHEN votes.use_id = 1 THEN votes.karma_delta ELSE 0 END
3. Change your timestampdiff to DATE_TRUNC('hour', now()) - DATE_TRUNC('hour', links.created) (you will need to then count the number of hours in the resulting interval. It would be much easier to compare timestamps)
4. Fix your GROUP BY and ORDER BY