Mysql 如何使用伪值对表进行内部联接

根据@scaisEdge发布的解决方案。我还有一个关于“内部连接”的问题。我试着用“pid”值加入它们。但sql表示“未知”

这是他的密码：

 SELECT SUBSTRING(`page_url`,-3) as pid 
  from `prop_log` 
  WHERE `page_url` REGEXP '[0-9]'
  group by SUBSTRING(`page_url`,-3)
  order by count(*)

这是我的：

SELECT prop_sid,SUBSTRING(`page_url`,-3) as pid 
from `prop_log` 
inner join prop_db2 on prop_db2.prop_id=pid
WHERE `page_url` REGEXP '[0-9]'
group by SUBSTRING(`page_url`,-3)
order by count(*) desc
limit 5

---

PS.prop_sid来自prop_db2

您不能在where（或on）条件下使用别名

SELECT prop_sid,SUBSTRING(`page_url`,-3) as pid 
from `prop_log` 
inner join prop_db2 on prop_db2.prop_id=SUBSTRING(`page_url`,-3)
WHERE `page_url` REGEXP '[0-9]'
group by SUBSTRING(`page_url`,-3)
order by count(*) desc
limit 5

允许在group by中的order by和某些mysql版本中使用别名，但在where中不允许使用别名

您还应该对不在GROUPBY中的列使用（伪）聚合函数

SELECT min(prop_sid),SUBSTRING(`page_url`,-3) as pid 
from `prop_log` 
inner join prop_db2 on prop_db2.prop_id=SUBSTRING(`page_url`,-3)
WHERE `page_url` REGEXP '[0-9]'
group by SUBSTRING(`page_url`,-3)
order by count(*) desc
limit 5

或者通过与查询一致的方式将列添加到组中

SELECT prop_sid,SUBSTRING(`page_url`,-3) as pid 
from `prop_log` 
inner join prop_db2 on prop_db2.prop_id=SUBSTRING(`page_url`,-3)
WHERE `page_url` REGEXP '[0-9]'
group by SUBSTRING(`page_url`,-3), prop_sid
order by count(*) desc
limit 5

---

我已经发布了一个回复，还有一些其他的建议。。希望就是你想要的

SELECT prop_sid, prop_db2.prop_id as pid 
from `prop_log` 
inner join prop_db2 on prop_db2.prop_id=SUBSTRING(`page_url`,-3)
WHERE `page_url` REGEXP '[0-9]'
group by prop_db2.prop_id
order by count(*) desc
limit 5