Question

我正在尝试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我所需的字段。

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_categories获取ID并在tutorial_comments中使用它。我想要做的最后一个输出就是得到每个教程列出的评论数量。

干杯，

雅各

Answer 1

雅各

您需要像这样添加group by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

Answer 2

这应该清理你的查询：

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

LEFT JOIN可防止教程消失但找不到匹配项我用JOIN条件明确了JOIN，这更容易理解，也更正确你的基本问题是你在括号内而不是在外面有计数注释的连接条件，这不能以这种方式工作。

Answer 3

你能试试这个：

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

MySQL查询COUNT输出

3 个答案: