MySQL Subquery Efficiency - mysql

Question

I have this query which adds a load of values to a 'stats' table. When the query runs it selects the values to fill the table in subqueries. I was wondering if this could be made any more efficiently or if I am doing something really wrong. I am not that familiar with MySQL so any help would be great :)
Here is the query:
UPDATE mediastats SET
mediastats_members = (SELECT count(*) FROM status WHERE status_media_id = :id),
mediastats_avscore = (SELECT AVG(status_rating) FROM status WHERE status_media_id = :id),
mediastats_done = (SELECT count(*) FROM status WHERE status_status = 'done' AND status_media_id = :id),
mediastats_doing = (SELECT count(*) FROM status WHERE status_status = 'doing' AND status_media_id = :id),
mediastats_redoing = (SELECT count(*) FROM status WHERE status_status = 'redoing' AND status_media_id = :id),
mediastats_dropped = (SELECT count(*) FROM status WHERE status_status = 'dropped' AND status_media_id = :id),
mediastats_wantto = (SELECT count(*) FROM status WHERE status_status = 'wantto' AND status_media_id = :id),
mediastats_wont = (SELECT count(*) FROM status WHERE status_status = 'wont' AND status_media_id = :id),
mediastats_stalled = (SELECT count(*) FROM status WHERE status_status = 'stalled' AND status_media_id = :id),
mediastats_rating_1 = (SELECT count(*) FROM status WHERE status_rating = 1 AND status_media_id = :id),
mediastats_rating_2 = (SELECT count(*) FROM status WHERE status_rating = 2 AND status_media_id = :id),
mediastats_rating_3 = (SELECT count(*) FROM status WHERE status_rating = 3 AND status_media_id = :id),
mediastats_rating_4 = (SELECT count(*) FROM status WHERE status_rating = 4 AND status_media_id = :id),
mediastats_rating_5 = (SELECT count(*) FROM status WHERE status_rating = 5 AND status_media_id = :id),
mediastats_rating_6 = (SELECT count(*) FROM status WHERE status_rating = 6 AND status_media_id = :id),
mediastats_rating_7 = (SELECT count(*) FROM status WHERE status_rating = 7 AND status_media_id = :id),
mediastats_rating_8 = (SELECT count(*) FROM status WHERE status_rating = 8 AND status_media_id = :id),
mediastats_rating_9 = (SELECT count(*) FROM status WHERE status_rating = 9 AND status_media_id = :id),
mediastats_rating_10 = (SELECT count(*) FROM status WHERE status_rating = 10 AND status_media_id = :id)
WHERE mediastats_media_id = :id
The :id is added from PHP.

Answer 1

Here's how I'd do it in PHP with PDO:
$sql = "
SELECT
COUNT(*) AS mediastats_members,
AVG(status_rating) AS mediastats_avscore,
SUM(status_status = 'done') AS mediastats_done,
SUM(status_status = 'doing') AS mediastats_doing,
SUM(status_status = 'redoing') AS mediastats_redoing,
SUM(status_status = 'dropped') AS mediastats_dropped,
SUM(status_status = 'wantto') AS mediastats_wantto,
SUM(status_status = 'wont') AS mediastats_wont,
SUM(status_status = 'stalled') AS mediastats_stalled,
SUM(status_rating = 1) AS mediastats_rating_1,
SUM(status_rating = 2) AS mediastats_rating_2,
SUM(status_rating = 3) AS mediastats_rating_3,
SUM(status_rating = 4) AS mediastats_rating_4,
SUM(status_rating = 5) AS mediastats_rating_5,
SUM(status_rating = 6) AS mediastats_rating_6,
SUM(status_rating = 7) AS mediastats_rating_7,
SUM(status_rating = 8) AS mediastats_rating_8,
SUM(status_rating = 9) AS mediastats_rating_9,
SUM(status_rating = 10) AS mediastats_rating_10
FROM status
WHERE status_media_id = :id";
$stmt = $pdo->prepare($sql);
$stmt->execute(array("id"=>$id));
$params = $stmt->fetch(PDO::FETCH_ASSOC);
This way you calculate all the aggregates in one pass of the table, instead of using a separate subquery for each count.
I'm using a trick of MySQL -- the SUM() of a boolean expression is equal to the COUNT() where the expression is true. This is because MySQL boolean expressions always return 0 or 1, and the SUM of 0's and 1's is equal to the COUNT of the 1's.
Then you can use the result from the above query as the parameters array to an UPDATE statement:
$sql = "
UPDATE mediastats SET
mediastats_members = :mediastats_members,
mediastats_avscore = :mediastats_avscore,
mediastats_done = :mediastats_done,
mediastats_doing = :mediastats_doing,
mediastats_redoing = :mediastats_redoing,
mediastats_dropped = :mediastats_dropped,
mediastats_wantto = :mediastats_wantto,
mediastats_wont = :mediastats_wont,
mediastats_stalled = :mediastats_stalled,
mediastats_rating_1 = :mediastats_rating_1,
mediastats_rating_2 = :mediastats_rating_2,
mediastats_rating_3 = :mediastats_rating_3,
mediastats_rating_4 = :mediastats_rating_4,
mediastats_rating_5 = :mediastats_rating_5,
mediastats_rating_6 = :mediastats_rating_6,
mediastats_rating_7 = :mediastats_rating_7,
mediastats_rating_8 = :mediastats_rating_8,
mediastats_rating_9 = :mediastats_rating_9,
mediastats_rating_10 = :mediastats_rating_10
WHERE mediastats_media_id = :id";
$stmt = $pdo->prepare($sql);
$params["id"] = $id;
$stmt->execute($params);
Since PHP 5.3.4, PDO accepts parameter array keys without the leading :. You need the colon when you declare the parameter placeholder in your query, but you don't need it in the array of values you supply to execute().

Answer 2

UPDATE (
SELECT status_media_id,
COUNT(*) AS cnt, AVG(status_rating) AS avg_rating,
SUM(status_status = 'done') AS cnt_done,
...
FROM status
WHERE status_media_id = :id
) s
JOIN mediastats ms
ON ms.mediastats_media_id = s.status_media_id
SET ms.mediastats_members = cnt,
ms.mediastats_avscore = avg_rating,
ms.mediastats_done = cnt_done,
...