多列mysql子查询

Question

我正在尝试这样做

SELECT 
    `projects`.*,
    (SELECT 
        COUNT(`leads`.`id`),
        `pixel`.`uuid`,
        `pixel`.`project_id`
     FROM `leads` 
     LEFT JOIN `pixel` ON `leads`.`pixel` = `pixel`.`uuid`
     WHERE `projects`.`id` = `pixel`.`project_id`
     ) as leads

FROM `projects`

但是我不能，因为我的子查询选择有不止一列，但是我必须拥有它，这样我才能进行联接，无论如何？ （我只需要计数）谢谢。

Answer 1

将correlated Subquery更改为Inner Join以显示subquery所有列

SELECT projects.*,
       a.*
FROM   projects P
       INNER JOIN (SELECT Count(leads.id) Cnt_id,
                          pixel.uuid,
                          pixel.project_id
                   FROM   leads
                          LEFT JOIN pixel
                                 ON leads.pixel = pixel.uuid) A
               ON projects.id = A.project_id 

Answer 2

我建议您尝试避免子查询：

SELECT
  projects.*,
  IFNUL(COUNT(leads.id).0) AS Cnt_id
FROM
  projects,
  LEFT JOIN pixel ON projects.id = pixel.project_id
  LEFT JOIN leads ON leads.pixel = pixel.uuid
GROUP BY
  projects.id

我怀疑这会快很多。

Answer 3

这就是答案

SELECT 
    `projects`.*,
    (SELECT 
        COUNT(`pixel`.`project_id`) 
    FROM `pixel` 
    WHERE `projects`.`id` = `pixel`.`project_id`) AS `num_pixels`,
    (SELECT COUNT(`leads`.`id`) FROM `leads`
                    LEFT JOIN `pixel` ON `leads`.`pixel` = `pixel`.`uuid`
                    WHERE `projects`.`id` = `pixel`.`project_id`) AS `num_leads`
FROM `projects`