[英]Why my query shows no errors, but also returns zero rows?
我已经编写了此查询,以获取尽可能多的行,其中包括用户+每个用户创建的电位计数+已转换的所有电位。 它是这样的:
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,因为这个答案向我解释了 ,我可以将查询合并为1。但是我得到0行。
我的表如下所示:
使用者:
+----+------+-------+
| ID | Name | Email |
+----+------+-------+
潜力:
+----+------+-------+------------+-----------+
| ID | Name | Email | FID_author | converted |
+----+------+-------+------------+-----------+
FID_author是外键,即用户ID。
我的查询返回0行,没有显示错误。 我究竟做错了什么?
编辑
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
我得到的结果几乎与预期的一样,但是问题是, cPotentials
在每一行中都包含1,这是错误的。 只有1个,那么可能有很多问题。
子查询缺少分组依据,最终使用左联接
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
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