mysql - 在选择语句中使用月份(日期)时出现sql左连接错误

Question

此代码正在运行:

select Date1,  Date2
from 
    (SELECT Date1 FROM Table1 GROUP BY Date1) t1
left join
    (SELECT Date2 FROM Table2 GROUP BY Date2) t2
on
    t1.Date1 = t2.Date2

但是我需要使用它提取 Month(...)，所以当我更改这样的代码时，我收到错误:

Unknown column 'Date1' in 'field list'

select Date1,  Date2
from 
    (SELECT Month(Date1) FROM Table1 GROUP BY Date1) t1
left join
    (SELECT Month(Date2) FROM Table2 GROUP BY Date2) t2
on
    t1.Date1 = t2.Date2

实际上代码更大，只有这部分代码不允许我继续..

Answer 1

内部选择查询中缺少月份的别名

select Date1,  Date2
from 
    (SELECT Month(Date1) as date1 --Alias missing Here
     FROM Table1 
     GROUP BY Date1) t1
left join
    (SELECT Month(Date2) as date2 --Alias missing here
     FROM Table2 
     GROUP BY Date2) t2
on
    t1.Date1 = t2.Date2