MySQL查询计数输出

我试图从同一查询中的另一个SELECT中获取信息，但是我不太确定如何获取所需的字段

SELECT t.`id`, t.`title`, t.`author`, t.`content`, ctitle, cid, comments

FROM `tutorials` AS `t`, 

  (
    SELECT tc.`id` as `cid`, tc.`title` as `ctitle` 
    FROM `tutorial_categories` AS `tc` 
    WHERE `title` LIKE '%category title'
  ) AS `c`,

  (
    SELECT COUNT(com.`id`) as `comments`
    FROM `tutorial_comments` AS `com`
    WHERE `tutorial_id` = c.cid
  ) as `comments`

WHERE t.`category` = c.`cid` AND t.`status` = '1'
ORDER BY `id` ASC

我正在尝试从

tutorial\u类别

中获取id，并在

tutorial\u注释

中使用它。作为最终输出，我所要做的就是计算每个教程列出的注释数量

干杯

雅各布你能试试这个吗：

SELECT t.`id`, t.`title`, t.`author`, t.`content`, c.title, c.cid, ct.comments
FROM `tutorials` AS `t`

LEFT OUTER JOIN (
    SELECT tc.`id` as `cid`, tc.`title` as `ctitle` 
    FROM `tutorial_categories` AS `tc` 
    WHERE `title` LIKE '%category title'
  ) AS `c` ON t.`category` = c.`cid` 

LEFT OUTER JOIN (
    SELECT COUNT(com.`id`) as `comments`
    FROM `tutorial_comments` AS `com`
    group by com.`id`
  ) as `ct` on  ct.`tutorial_id` = c.cid

WHERE t.`status` = '1'
ORDER BY `id` ASC

你能试试这个吗

SELECT t.`id`, t.`title`, t.`author`, t.`content`, c.title, c.cid, ct.comments
FROM `tutorials` AS `t`

LEFT OUTER JOIN (
    SELECT tc.`id` as `cid`, tc.`title` as `ctitle` 
    FROM `tutorial_categories` AS `tc` 
    WHERE `title` LIKE '%category title'
  ) AS `c` ON t.`category` = c.`cid` 

LEFT OUTER JOIN (
    SELECT COUNT(com.`id`) as `comments`
    FROM `tutorial_comments` AS `com`
    group by com.`id`
  ) as `ct` on  ct.`tutorial_id` = c.cid

WHERE t.`status` = '1'
ORDER BY `id` ASC

雅各布

您需要像这样添加一个GROUPBY子句

select t.id, t.tilte, t.author, t.content, count(com.id) as comments
from tutorials as t
   join tutotials_categories as cat
      on t.category = cat.id
   join tutorials_comments as com
      on com.tutorial_id = t.id
where cat.title like'%category title'
   and t.status = 1
group by com.id
order by t.id asc

我使用了ansi连接形式

您需要像这样添加一个GROUPBY子句

select t.id, t.tilte, t.author, t.content, count(com.id) as comments
from tutorials as t
   join tutotials_categories as cat
      on t.category = cat.id
   join tutorials_comments as com
      on com.tutorial_id = t.id
where cat.title like'%category title'
   and t.status = 1
group by com.id
order by t.id asc

---

我使用了ansi连接表单

这应该可以清理您的查询：

SELECT t.id, t.title, t.author, t.content, c.ctitle, c.cid, com.comments
FROM   tutorials AS t
LEFT   JOIN (
    SELECT tutorial_id, COUNT(com.id) as comments
    FROM   tutorial_comments AS com
    GROUP  BY 1
    )  AS com ON com.tutorial_id = t.category
LEFT   JOIN (
    SELECT tc.id as cid, tc.title as ctitle 
    FROM   tutorial_categories AS tc 
    WHERE  title LIKE '%category title'
    )  AS c ON t.category = c.cid
WHERE  t.status = '1'
ORDER  BY t.id

左连接可防止找不到匹配项的教程消失。
我用连接条件进行了显式连接，这更容易理解，也是正确的方法。

---

您的主要问题是，您的计数注释的连接条件在括号内，而不是在括号外，这样做是行不通的。

这应该会清理您的查询：

SELECT t.id, t.title, t.author, t.content, c.ctitle, c.cid, com.comments
FROM   tutorials AS t
LEFT   JOIN (
    SELECT tutorial_id, COUNT(com.id) as comments
    FROM   tutorial_comments AS com
    GROUP  BY 1
    )  AS com ON com.tutorial_id = t.category
LEFT   JOIN (
    SELECT tc.id as cid, tc.title as ctitle 
    FROM   tutorial_categories AS tc 
    WHERE  title LIKE '%category title'
    )  AS c ON t.category = c.cid
WHERE  t.status = '1'
ORDER  BY t.id

左连接可防止找不到匹配项的教程消失。
我用连接条件进行了显式连接，这更容易理解，也是正确的方法。

---

您的主要问题是，您在括号内而不是括号外有计数的注释的连接条件，这无法实现。

现在它只显示有注释的结果，而不是每个类别的所有结果。很抱歉，我没有理解您的意思。您可以尝试“左连接”来显示那些没有注释的教程，还可以按类别排序以对结果集进行排序。顺便说一句，我想你可以试试@erwin的脚本。现在它只显示有评论的结果，而不是每个类别的所有结果。很抱歉，我没有理解你的意思。您可以尝试“左连接”来显示那些没有注释的教程，还可以按类别排序以对结果集进行排序。顺便说一句，我想你可以试试@erwin的脚本。