Question

我已经编写了这个查询，以获得与用户一样多的行数+每个用户创建的潜在数量+已转换的所有潜力。这就是它的样子：

SELECT u.*, p.allPotentials, pc.cPotentials 
   FROM os_user u
JOIN (SELECT FID_author, count(*) allPotentials FROM os_potential) p 
   ON p.FID_author = u.ID 
JOIN (SELECT converted, FID_author, count(*) cPotentials FROM os_potential) pc 
   ON p.FID_author = u.ID AND pc.converted = 1

我正在尝试使用不相关的子查询作为this answer explained me，我可以将我的查询组合成1.但是我得到0行。

我的表格如下：

用户：

+----+------+-------+
| ID | Name | Email |
+----+------+-------+

势：

+----+------+-------+------------+-----------+
| ID | Name | Email | FID_author | converted |
+----+------+-------+------------+-----------+

FID_author是外键，即用户ID。

我的查询返回0行并且没有显示错误。我做错了什么？

修改

到目前为止我的查询：

SELECT u.*, p.allPotentials, pc.cPotentials 
   FROM os_user u
LEFT JOIN (SELECT FID_author, count(*) allPotentials 
   FROM os_potential GROUP BY FID_author) p 
   ON p.FID_author = u.ID 
LEFT JOIN (SELECT converted, FID_author, count(*) cPotentials 
   FROM os_potential GROUP BY FID_author) pc 
   ON p.FID_author = u.ID 
   AND pc.converted = 1 
GROUP BY u.ID

我的结果几乎与预期一致，但问题是，cPotentials每行包含1，这是错误的。有很多很多只有1.哪里可能是问题？

Answer 1

在子查询中缺少组，并最终使用左连接

SELECT u.*, p.allPotentials, pc.cPotentials 
 FROM os_user u
LEFT JOIN (SELECT FID_author, count(*) allPotentials FROM os_potential 
                  GROUP BY FID_author) p 
 ON p.FID_author = u.ID 
LEFT JOIN (SELECT converted, FID_author, count(*) cPotentials FROM os_potential 
                   GROUP BY converted,FID_author) pc 
 ON pc.FID_author = u.ID AND pc.converted = 1

为什么我的查询显示没有错误，但也返回零行？

1 个答案: