How to get photo of the day?

I have two tables in MySQL database:

photos:

PID - PhotoID [PK], 
DateOf - DateTime of uploading, 
UID -UserID (owner of the photo)

ratings:

WhoUID - UserID who rated, 
DateOf - DateTime of rate, 
RatingValue - +1 or -1 (positive or negative), 
RatingStrength - coefficient (different for each user who vote)
PID - PhotoID, [FK]

Real rating value = RatingValue * RatingStrength

What are possibilities to get "Photo of the day"?

Rules, for example:

• photo of the day must be on site at least 24 hours (since uploaded time)
• photo of the day must have at least 10 votes
• photo of the day is the photo with maximum Real rating value in 24 hours since uploaded time
• new photo of the day must not be already in photo_of_day table

UPD1. 10 votes means - at least 10 records in table ratings for each photo

UPD2. Is it possible to get 'photo of the day' for exact datetime? For exampl开发者_高级运维e, how can I get photo of the day for '2011-03-11', or '2011-01-25' ?

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select p.PID from photos p, ratings r where
r.PID = p.PID and                             ; Link ratings to photo
p.DateOf >= '$day' and p.DateOf <= '$day' and ; Get the photos uploaded on the specified date
datediff(p.DateOf, now()) > 1 and             ; photo of the day must be on site at least 24 hours
count(r.*) >= 10 and                          ; photo should have at least 10 ratings
not exists(select p.PID from photo_of_day)    ; photo should not appear in photo_of_day
group by p.PID                                ; group the results by PID
order by sum(r.RatingValue*r.RatingStrength) desc ; order descending by RealRating
limit 1                                       ; limit the results to only one

This query probably takes a while, so it makes sense to not do this on every page request. You store the result in photo_of_day once by a script that runs once at midnight.

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Something like this. I'm not sure about 'new photo of the day must not be already in photo_of_day table', but try this one -

SET @exact_datetime = NOW();

SELECT p.*, SUM(r.RatingValue * r.RatingStrength) AS real_rating FROM photos p
  JOIN ratings r
    ON p.PhotoID = r.PhotoID
WHERE
  p.DateOf <= @exact_datetime - INTERVAL 1 DAY
GROUP BY
  p.PhotoID
HAVING
  count(*) >= 10
ORDER BY
  real_rating DESC
LIMIT 1