这个问题是关于在调用CONCAT
并将其存储为别名时定义容量/最大长度的可能性。
我有一个相当复杂的MySQL查询,它使用Common Table Expressions(CTE)来建模注释。它创建一个新变量path
,该变量由评论的分数(投票数)和ID组成,并用逗号分隔,并使用CONCAT
与其父路径连接起来。这允许按分数对线程内的注释进行排序。
A path
看起来像000010,000005,000014,000008
,表示ID为8
的评论的得分为14
,其父级(其本身没有父级)的ID为5
,得分为10
。具有path
这种格式的所有注释都可以按照我的需要对它们进行排序。
最重要的是,最初path
仅包含一个ID为ID的乐谱,在递归调用中,当我们探访孩子时,我们将继续串联成越来越长的路径。
但是,似乎最初对CONCAT
的调用立即将所有后续串联的大小限制为15,这是最长的初始串联,因此它们仅在15个字符之后被剪切。使初始串联的长度大于15,将随后的串联限制为最长的初始串联(因此实际上不会串联任何东西)。
[目前,我已经解决了这个问题,首先在右边填充了很多零,然后在递归调用中将其删除。但是,这使用了正则表达式,即使很简单,我也担心它对性能不好。
可以通过初始调用CONCAT
来定义所创建的别名变量的容量/最大长度是什么?
这是所进行的查询:
WITH RECURSIVE first_comments (id, content, parent_id, user_id, created, votes, path) AS (
(
SELECT r.id, r.content, r.parent_id, r.user_id, r.created, r.votes, CONCAT_WS(",", LPAD(r.votes,6,0), LPAD(r.id,6,0), LPAD(0,243,0)) as path
FROM (
SELECT c.id, c.content, c.parent_id, c.user_id, c.created, COUNT(DISTINCT v.id) AS votes
FROM comments AS c
LEFT JOIN comment_votes AS v ON c.id = v.comment_id
WHERE c.post_id = ? AND c.parent_id IS NULL
GROUP BY c.id
) as r
)
UNION ALL
(
SELECT r.id, r.content, r.parent_id, r.user_id, r.created, r.votes, CONCAT_WS(",", REGEXP_REPLACE(fle.path, ",[0]+$", ""), LPAD(r.votes,6,0), LPAD(r.id,6,0)) as path
FROM first_comments AS fle
JOIN (
SELECT c.id, c.content, c.parent_id, c.user_id, c.created, COUNT(DISTINCT v.id) AS votes
FROM comments AS c
LEFT JOIN comment_votes AS v ON c.id = v.comment_id
WHERE c.post_id = ?
GROUP BY c.id
) AS r ON fle.id = r.parent_id
)
)
SELECT id, content, parent_id, user_id, path, created, votes FROM first_comments
ORDER BY pat
((受:Order comments by thread path and by number of total votes启发)
[最初,我用path
创建CONCAT_WS(",", LPAD(r.votes,6,0), LPAD(r.id,6,0), LPAD(0,243,0)) as path
,这将创建包含最上面的注释的分数和ID(无父级),并在右边填充243零的路径。所以例如000010,000005,0...0
代表ID为5
的最上面的评论。
然后递归(但仅在第一次递归调用时有效,因为此后模式从不匹配),我们使用正则表达式删除所有尾随零,包括最后一个逗号,并添加此注释的分数和ID:CONCAT_WS(",", REGEXP_REPLACE(fle.path, ",[0]+$", ""), LPAD(r.votes,6,0), LPAD(r.id,6,0)) as path
。
因此,最好在path
的初始定义中添加一些内容,而不是这种解决方法。但是我不知道还有什么其他可能和更好的方法?
感谢您的任何帮助和想法!
//编辑:在GMB的帮助下,并进行了少量添加,问题已得到解决(并得以简化),请参阅我在可接受答案下的评论。
如何将路径附加到JSON数组而不是字符串中?这无缝地克服了您遇到的问题,您仍然可以order by
。
所以:
WITH RECURSIVE first_comments (id, content, parent_id, user_id, created, votes, js_path) AS (
SELECT
c.id,
c.content,
c.parent_id,
c.user_id,
c.created,
COUNT(DISTINCT v.id) AS votes,
JSON_ARRAY(LPAD(COUNT(DISTINCT v.id), 6, 0), LPAD(c.id, 6, 0)) as js_path
FROM comments AS c
LEFT JOIN comment_votes AS v ON c.id = v.comment_id
WHERE c.post_id = ? AND c.parent_id IS NULL
GROUP BY c.id
UNION ALL
SELECT
r.id,
r.content,
r.parent_id,
r.user_id,
r.created,
r.votes,
JSON_ARRAY_APPEND(
fle.js_path,
'$', LPAD(r.votes, 6, 0),
'$', LPAD(r.id, 6, 0)
) as js_path
FROM first_comments AS fle
JOIN (
SELECT
c.id,
c.content,
c.parent_id,
c.user_id,
c.created,
COUNT(DISTINCT v.id) AS votes
FROM comments AS c
LEFT JOIN comment_votes AS v ON c.id = v.comment_id
WHERE c.post_id = ?
GROUP BY c.id
) AS r ON fle.id = r.parent_id
)
SELECT id, content, parent_id, user_id, js_path, created, votes
FROM first_comments
ORDER BY js_path
请注意,我将查询简化如下:
递归查询的锚点中不需要子查询
[union all
不需要在两个查询之间加括号