php - 如何正确使用 MySQL join/count

Question

所以我有以下查询：

'SELECT *, upload.id AS id, report.id AS report_id, (SELECT COUNT(*) 
    FROM upload WHERE report.upload_id = upload.id) AS nums FROM upload 
    LEFT JOIN report ON upload.id=report.upload_id WHERE private="0" '

我对如何计算每次上传的报告有疑问。此查询需要计算给定上传的所有报告，并在获取时返回所有上传。由于某种原因，每次插入新报告而不是添加到总数中时，我都会重复上传。见下图：

请注意，对于与给定上传相关的每个报告，console (1).png 如何显示三次......真的我希望它显示一次，然后侧面的计数应该是（3）。任何帮助将非常感激！！

Answer 1

选择 count(upload.id)，report.id from report，上传 LEFT JOIN report ON upload.id=report.upload_id WHERE private="0" group by report.id

Answer 2

如果您只需要每次上传的报告数量，则不需要加入它们，您可以这样做：

SELECT upload.*, 
      (SELECT COUNT(*) FROM report WHERE report.upload_id = upload.id) AS nums 
FROM upload 

或者你可以这样做：

SELECT upload.id, upload.name, count(*) as nums
FROM upload 
  INNER JOIN report ON report.upload_id = upload.id
GROUP BY upload.id, upload.name

这将返回所有带有报告的上传。要获取包含或不包含报告的所有上传，您需要左连接：

SELECT upload.id, upload.name, count(report.id) as nums
FROM upload 
  left JOIN report ON report.upload_id = upload.id
GROUP BY upload.id, upload.name

这是一个带有查询的SQL Fiddle 。

Answer 3

用于测试的SQL Fiddle 。

只需使用左连接并计算report.upload_ids

select u.filename, u.filesize, COUNT(r.upload_id) as reports
from upload u
left join report r on u.id=r.upload_id
group by u.id, u.filename, u.filesize

我漏掉了where private = "0"，因为你没有指定它属于哪里。

Answer 4

SELECT 
  upload.id, 
  upload.name, 
  count(1) as nums
FROM 
  upload 
LEFT OUTER JOIN 
  report ON
  report.upload_id = upload.id
GROUP BY 
  upload.id,
  upload.name