php – 添加一个表来查询和计算数据SQL
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我尝试从4个表中选择数据(最后一个表需要计算数据)
我的MySQL表结构
用户
id
username
图片
id
user_id
image
user_follow
id
user_id
follow_id
评论
id
user_id
image_id
text
我有这个SQL查询:
$sql = "SELECT u.username as user, i.image as user_image, p.image, p.date
FROM users u
LEFT JOIN user_follow f ON u.id = f.follow_id
LEFT JOIN images p ON p.user_id = u.id
LEFT JOIN images i ON i.id = (SELECT b.id FROM images AS b where p.user_id = b.user_id ORDER BY b.id DESC LIMIT 1)
WHERE f.user_id = 3 OR p.user_id = 3
ORDER BY p.date DESC";
此行返回用户当前图像(最后一张图像)
LEFT JOIN images i ON i.id = (SELECT b.id FROM images AS b where p.user_id = b.user_id ORDER BY b.id DESC LIMIT 1)
它返回我和我的朋友的所有图像
[0] => Array
(
[user] => 8888
[user_image] => second.jpg
[image] => second.jpg
[date] => 2012-01-24 14:42:27
)
[1] => Array
(
[user] => 8888
[user_image] => second.jpg
[image] => first.jpg
[date] => 2012-01-24 14:42:27
)
[2] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => ax46l7v7vugnesk10whk_339.jpg
[date] => 2012-01-24 01:54:19
)
[3] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => aaaaaaaa.jpg
[date] => 2012-01-24 01:49:57
)
我试着补充一下
left join commentaries c ON c.user_id = u.id
结果是
[2] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => ax46l7v7vugnesk10whk_339.jpg
[date] => 2012-01-24 01:54:19
[id] => 1
)
[3] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => ax46l7v7vugnesk10whk_339.jpg
[date] => 2012-01-24 01:54:19
[id] => 2
)
[4] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => aaaaaaaa.jpg
[date] => 2012-01-24 01:49:57
[id] => 1
)
[5] => Array
(
[user] => 3333
[user_image] => ax46l7v7vugnesk10whk_339.jpg
[image] => aaaaaaaa.jpg
[date] => 2012-01-24 01:49:57
[id] => 2
)
如果有评论,则重复用户(顺便说一句[用户] => 3333在示例中有2条评论)
我正在尝试添加一个表“评论”并计算每个图片(来自我和我的朋友)有多少评论如果没有这样的$user_id的评论然后返回0
解决方法:
您需要使用GROUP BY来计算组中的行数(在您的情况下,每个图像的注释).这个查询应该做的伎俩:
SELECT u.username as user, i.image as user_image, p.image, p.date,
COALESCE ( imgcount.cnt, 0 ) as comments
FROM users u
LEFT JOIN user_follow f ON u.id = f.follow_id
LEFT JOIN images p ON p.user_id = u.id
LEFT JOIN images i ON i.id = (SELECT b.id FROM images AS b where p.user_id = b.user_id ORDER BY b.id DESC LIMIT 1)
LEFT JOIN
( SELECT image_id, COUNT(*) as cnt FROM
commentaries
GROUP BY image_id ) imgcount
ON p.id = imgcount.image_id
WHERE f.user_id = 3 OR p.user_id = 3
ORDER BY p.date DESC
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