mySQL Query design - calculating a vote score for multiple content items

I have a content items table structured like

|  contentid |   message     |    categoryid  |  userid  |    dateadded | etc.. 
     15          foo bar            3             4           somedate
     16          more foo bar       3             4           somedate
     16          foo stuff          3             4           somedate

and a votes table, where direction = 1 = an up vote, and = 2 being a down vote.

|  voteid   |  contentid |  userid  |  direction |    dateadded
    7             15          4            1           some date
    8             15          6            1           some date
    9             15          17           2           some date

And I'd like to select a set of content items, having an additional column on the end with its calculated score based on the votes in the votes table.

Previously, I had a 'score' column attached to the content table, and 开发者_如何学JAVAeach time a vote was cast, it would update its score. This was done so I wouldnt have to have a more complex query to calculate scores on each SELECT, but I'd like to change this now.

This votes table was designed a while ago, so if changing all the votes values to something other than 1 or 2 (perhaps -1 for a downvote) would make it easier, I will update the entire table.

What would the query be to pull all content items, each with a score in a calculated column?

Assuming the vote "direction" represents up and down votes:

SELECT i.contentid, 
       SUM(CASE WHEN v.direction = 1 THEN 1
                WHEN v.direction = 2 THEN -1
                ELSE 0 END) AS Votes
    FROM items i
        LEFT JOIN votes v
            ON i.contentid = v.contentid
    GROUP BY i.contentid
    HAVING SUM(CASE WHEN v.direction = 1 THEN 1
                WHEN v.direction = 2 THEN -1
                ELSE 0 END) > -3

SELECT
  items.*,
  SUM(direction = 1) - SUM(direction = 2) AS score
FROM items
LEFT JOIN votes USING (contentid)
GROUP BY contentid

The reason this works is because a true comparison evaluates to 1 and a false one to 0.