MySQL子查询效率
我有一个查询,它向一个“stats”表添加了一堆值。当查询运行时,它选择要在子查询中填充表的值。我想知道这是否可以更有效地进行,或者我是否真的做错了什么。我对MySQL不太熟悉,所以任何帮助都会很好:) 以下是查询:MySQL子查询效率,mysql,performance,Mysql,Performance,我有一个查询,它向一个“stats”表添加了一堆值。当查询运行时,它选择要在子查询中填充表的值。我想知道这是否可以更有效地进行,或者我是否真的做错了什么。我对MySQL不太熟悉,所以任何帮助都会很好:) 以下是查询: UPDATE mediastats SET mediastats_members = (SELECT count(*) FROM status WHERE status_media_id = :id), mediastats_avscore = (SELECT A
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
:id是从PHP添加的。下面是我在PHP中使用PDO的方法:
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,
...
$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);
通过这种方式,您可以在表的一个过程中计算所有聚合,而不是对每个计数使用单独的子查询
我使用的是MySQL的一个技巧——布尔表达式的SUM()等于COUNT(),其中表达式为true。这是因为MySQL布尔表达式总是返回0或1,并且0和1的总和等于1的计数
然后,您可以将上述查询的结果用作UPDATE语句的参数数组:
$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);
从PHP5.3.4开始,PDO接受参数数组键,而不使用前导的
:
。在查询中声明参数占位符时需要冒号,但在提供给execute()的值数组中不需要冒号 谢谢,太棒了:)这种方法比原来的方法有什么优点?优点是它可以一次计算出整个表中的所有计数。