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我正在尝试获取与我下载的每个帖子相关的最新 1 或 2 条评论,有点像 Instagram 所做的,因为它们显示每个帖子的最新 3 条评论,到目前为止,我得到了帖子和喜欢计数。
现在我需要做的就是弄清楚如何获得最新评论,不太确定如何处理它,这就是为什么我希望有更多专业知识的人可以帮助我!
这是我当前的查询:
(SELECT
P.uuid,
P.caption,
P.imageHeight,
P.path,
P.date,
U.id,
U.fullname,
U.coverImage,
U.bio,
U.username,
U.profileImage,
coalesce(Activity.LikeCNT,0),
Activity.CurrentUserLiked
FROM USERS AS U
INNER JOIN Posts AS P
ON P.id = U.id
LEFT JOIN (SELECT COUNT(DISTINCT Activity.uuidPost) LikeCNT, Activity.uuidPost, Activity.id, sum(CASE WHEN Activity.id = $id then 1 else 0 end) as CurrentUserLiked
FROM Activity Activity
WHERE type = 'like'
GROUP BY Activity.uuidPost) Activity
ON Activity.uuidPost = P.uuid
AND Activity.id = U.id
WHERE U.id = $id)
UNION
(SELECT
P.uuid,
P.caption,
P.imageHeight,
P.path,
P.date,
U.id,
U.fullname,
U.coverImage,
U.bio,
U.username,
U.profileImage,
coalesce(Activity.LikeCNT,0),
Activity.CurrentUserLiked
FROM Activity AS A
INNER JOIN USERS AS U
ON A.IdOtherUser=U.id
INNER JOIN Posts AS P
ON P.id = U.id
LEFT JOIN (SELECT COUNT(DISTINCT Activity.uuidPost) LikeCNT, Activity.uuidPost, Activity.id, sum(CASE WHEN Activity.id = $id then 1 else 0 end) as CurrentUserLiked
FROM Activity Activity
WHERE type = 'like'
GROUP BY Activity.uuidPost) Activity
ON Activity.uuidPost = P.uuid
AND Activity.id = U.id
WHERE A.id = $id)
ORDER BY date DESC
LIMIT 0, 5
Activity
,那么我有一列
comment
其中存储评论文本,然后“类型”等于“评论”。
Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8_unicode_ci,IMPLICIT) for operation '='
SELECT Posts.id,
Posts.uuid,
Posts.caption,
Posts.path,
Posts.date,
USERS.id,
USERS.username,
USERS.fullname,
USERS.profileImage,
coalesce(A.LikeCNT,0),
com.comment
FROM Posts
INNER JOIN USERS
ON Posts.id = 145
AND USERS.id = 145
LEFT JOIN (SELECT COUNT(A.uuidPost) LikeCNT, A.UUIDPost
FROM Activity A
WHERE type = 'like'
GROUP BY A.UUIDPOST) A
on A.UUIDPost=Posts.uuid
LEFT JOIN (SELECT comment, UUIDPOST, @row_num := IF(@prev_value=UUIDPOST,@row_num+1,1) as row_number,@prev_value := UUIDPOST
FROM Activity
CROSS JOIN (SELECT @row_num := 1) x
CROSS JOIN (SELECT @prev_value := '') y
WHERE type = 'comment'
ORDER BY UUIDPOST, date DESC) Com
ON Com.UUIIDPOSt = Posts.UUID
AND row_number <= 2
ORDER BY date DESC
LIMIT 0, 5
----------------------------------------------------------
| id | int(11) | | not null |
| uuid | varchar(100) | utf8_unicode_ci | not null |
| imageLink | varchar(500) | utf8_unicode_ci | not null |
| date | timestamp | | not null |
----------------------------------------------------------
-------------------------------------------------------------
| id | int(11) | | not null |
| username | varchar(100) | utf8_unicode_ci | not null |
| profileImage | varchar(500) | utf8_unicode_ci | not null |
| date | timestamp | | not null |
-------------------------------------------------------------
----------------------------------------------------------
| id | int(11) | | not null |
| uuid | varchar(100) | utf8_unicode_ci | not null |
| uuidPost | varchar(100) | utf8_unicode_ci | not null |
| type | varchar(50) | utf8_unicode_ci | not null |
| commentText | varchar(500) | utf8_unicode_ci | not null |
| date | timestamp | | not null |
----------------------------------------------------------
最佳答案
这个错误信息
Illegal mix of collations (utf8_general_ci,IMPLICIT) and(utf8_unicode_ci,IMPLICIT) for operation '='
CREATE TABLE Posts
(
`id` int,
`uuid` varchar(7) collate utf8_unicode_ci,
`imageLink` varchar(9) collate utf8_unicode_ci,
`date` datetime
);
INSERT INTO Posts(`id`, `uuid`, `imageLink`, `date`)
VALUES
(145, 'abcdefg', 'blah blah', '2016-10-10 00:00:00') ;
CREATE TABLE USERS
(
`id` int,
`username` varchar(15) collate utf8_unicode_ci,
`profileImage` varchar(12) collate utf8_unicode_ci,
`date` datetime
) ;
INSERT INTO USERS(`id`, `username`, `profileImage`, `date`)
VALUES
(145, 'used_by_already', 'blah de blah', '2014-01-03 00:00:00') ;
CREATE TABLE Activity
(
`id` int,
`uuid` varchar(4) collate utf8_unicode_ci,
`uuidPost` varchar(7) collate utf8_unicode_ci,
`type` varchar(40) collate utf8_unicode_ci,
`commentText` varchar(11) collate utf8_unicode_ci, `date` datetime
) ;
INSERT INTO Activity (`id`, `uuid`, `uuidPost`, `type`, `commentText`, `date`)
VALUES
(345, 'a100', 'abcdefg', 'comment', 'lah lha ha', '2016-07-05 00:00:00'),
(456, 'a101', 'abcdefg', 'comment', 'lah lah lah', '2016-07-06 00:00:00'),
(567, 'a102', 'abcdefg', 'comment', 'lha lha ha', '2016-07-07 00:00:00'),
(678, 'a103', 'abcdefg', 'comment', 'ha lah lah', '2016-07-08 00:00:00'),
(789, 'a104', 'abcdefg', 'comment', 'hla lah lah', '2016-07-09 00:00:00') ;
[SQL 标准行为:每个 Post 查询 2 行]
SELECT
Posts.id
, Posts.uuid
, rcom.uuidPost
, rcom.commentText
, rcom.`date` commentDate
#, Posts.caption
#, Posts.path
, Posts.`date`
, USERS.id
, USERS.username
#, USERS.fullname
, USERS.profileImage
, COALESCE(A.LikeCNT, 0) num_likes
FROM Posts
INNER JOIN USERS ON Posts.id = 145
AND USERS.id = 145
LEFT JOIN (
SELECT
COUNT(A.uuidPost) LikeCNT
, A.UUIDPost
FROM Activity A
WHERE type = 'like'
GROUP BY
A.UUIDPOST
) A ON A.UUIDPost = Posts.uuid
LEFT JOIN (
SELECT
@row_num := IF(@prev_value=UUIDPOST,@row_num+1,1) as row_number
, commentText
, uuidPost
, `date`
, @prev_value := UUIDPOST
FROM Activity
CROSS JOIN ( SELECT @row_num := 1, @prev_value := '' collate utf8_unicode_ci ) xy
WHERE type = 'comment'
ORDER BY
uuidPost
, `date` DESC
) rcom ON rcom.uuidPost = Posts.UUID
AND rcom.row_number <= 2
ORDER BY
posts.`date` DESC
;
See a working demonstration of this query at SQLFiddle
| id | uuid | uuidPost | commentText | date | date | id | username | profileImage | num_likes |
|-----|---------|----------|-------------|------------------------|---------------------------|-----|-----------------|--------------|-----------|
| 145 | abcdefg | abcdefg | hla lah lah | July, 09 2016 00:00:00 | October, 10 2016 00:00:00 | 145 | used_by_already | blah de blah | 0 |
| 145 | abcdefg | abcdefg | ha lah lah | July, 08 2016 00:00:00 | October, 10 2016 00:00:00 | 145 | used_by_already | blah de blah | 0 |
正如预期的那样,有 2 行。一行是最近的评论,另一行是下一个最近的评论。这是 SQL 的正常行为,在此答案下添加注释之前,问题的读者会认为这种正常行为是可以接受的。
SELECT
Posts.id
, Posts.uuid
, max(case when rcom.row_number = 1 then rcom.commentText end) Comment_one
, max(case when rcom.row_number = 2 then rcom.commentText end) Comment_two
#, Posts.caption
#, Posts.path
, Posts.`date`
, USERS.id
, USERS.username
#, USERS.fullname
, USERS.profileImage
, COALESCE(A.LikeCNT, 0) num_likes
FROM Posts
INNER JOIN USERS ON Posts.id = 145
AND USERS.id = 145
LEFT JOIN (
SELECT
COUNT(A.uuidPost) LikeCNT
, A.UUIDPost
FROM Activity A
WHERE type = 'like'
GROUP BY
A.UUIDPOST
) A ON A.UUIDPost = Posts.uuid
LEFT JOIN (
SELECT
@row_num := IF(@prev_value=UUIDPOST,@row_num+1,1) as row_number
, commentText
, uuidPost
, `date`
, @prev_value := UUIDPOST
FROM Activity
CROSS JOIN ( SELECT @row_num := 1, @prev_value := '' collate utf8_unicode_ci ) xy
WHERE type = 'comment'
ORDER BY
uuidPost
, `date` DESC
) rcom ON rcom.uuidPost = Posts.UUID
AND rcom.row_number <= 2
GROUP BY
Posts.id
, Posts.uuid
#, Posts.caption
#, Posts.path
, Posts.`date`
, USERS.id
, USERS.username
#, USERS.fullname
, USERS.profileImage
, COALESCE(A.LikeCNT, 0)
ORDER BY
posts.`date` DESC
;
See the second query working at SQLFiddle
| id | uuid | Comment_one | Comment_two | date | id | username | profileImage | num_likes |
|-----|---------|-------------|-------------|---------------------------|-----|-----------------|--------------|-----------|
| 145 | abcdefg | hla lah lah | ha lah lah | October, 10 2016 00:00:00 | 145 | used_by_already | blah de blah | 0 |
SELECT
Posts.id
, Posts.uuid
, group_concat(rcom.commentText) Comments_two_concatenated
#, Posts.caption
#, Posts.path
, Posts.`date`
, USERS.id
, USERS.username
#, USERS.fullname
, USERS.profileImage
, COALESCE(A.LikeCNT, 0) num_likes
FROM Posts
INNER JOIN USERS ON Posts.id = 145
AND USERS.id = 145
LEFT JOIN (
SELECT
COUNT(A.uuidPost) LikeCNT
, A.UUIDPost
FROM Activity A
WHERE type = 'like'
GROUP BY
A.UUIDPOST
) A ON A.UUIDPost = Posts.uuid
LEFT JOIN (
SELECT
@row_num := IF(@prev_value=UUIDPOST,@row_num+1,1) as row_number
, commentText
, uuidPost
, `date`
, @prev_value := UUIDPOST
FROM Activity
CROSS JOIN ( SELECT @row_num := 1, @prev_value := '' collate utf8_unicode_ci ) xy
WHERE type = 'comment'
ORDER BY
uuidPost
, `date` DESC
) rcom ON rcom.uuidPost = Posts.UUID
AND rcom.row_number <= 2
GROUP BY
Posts.id
, Posts.uuid
#, Posts.caption
#, Posts.path
, Posts.`date`
, USERS.id
, USERS.username
#, USERS.fullname
, USERS.profileImage
, COALESCE(A.LikeCNT, 0)
ORDER BY
posts.`date` DESC
See this third query working at SQLFiddle
| id | uuid | Comments_two_concatenated | date | id | username | profileImage | num_likes |
|-----|---------|---------------------------|---------------------------|-----|-----------------|--------------|-----------|
| 145 | abcdefg | hla lah lah,ha lah lah | October, 10 2016 00:00:00 | 145 | used_by_already | blah de blah | 0 |
LEFT JOIN (
SELECT
COUNT(*) FollowCNT
, IdOtherUser
FROM Activity
WHERE type = 'Follow'
GROUP BY
IdOtherUser
) F ON USERS.id = F.IdOtherUser
虽然添加另一个子查询可能会解决您对更多信息的渴望,但整体查询可能会随着数据的增长而变慢。一旦确定了您真正需要的功能,就值得考虑在这些表上需要哪些索引。 (我相信您会被建议单独询问该建议,如果您确实确保包含 1. 表的完整 DDL 和 2. 查询的解释计划。)
关于php - MYSQL 查询 - 获取与帖子相关的最新评论,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40268501/
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