sql - 在 JOIN 的 ON 子句中使用别名

Question

Stack Overflow 新手(以及一般编码)。

我做了一些研究，但无法找到以下问题的答案:

如何根据应用于维度的函数结果而不是维度本身连接两个表？

即我想将以下两个表连接到函数 lower() 的小写结果上，而不是按原样连接大小写不明确的维度。

SELECT
lower(first_name) as firstname
,lower(last_name) as lastname
,lower(email) as email1
,total_donated
From BensData.Donations As a

JOIN EACH

(Select
lower(first_name) as first
,lower(last_name) as last
,lower(email) as email2
,sum(amount) as total_donated
From BensData.Donations 
GROUP BY email2, first, last) As b

ON a.email1=b.email2 AND a.firstname=b.first AND a.lastname=b.last

它不允许我加入在第一个表 (a) 中创建的别名，但是，如果我加入表 a 中的原始维度(名字和姓氏)，那么结果将基于大小写不明确的维度，并给出不想要的结果。

我希望这是清楚的。

感谢您的帮助!

Answer 1

尝试使用两个子查询，如下所示:

SELECT
a.firstname
,a.lastname
,a.email1
,a.total_donated
FROM

(SELECT
lower(first_name) as firstname
,lower(last_name) as lastname
,lower(email) as email1
,total_donated
From BensData.Donations) As a

JOIN EACH

(Select
lower(first_name) as first
,lower(last_name) as last
,lower(email) as email2
,sum(amount) as total_donated
From BensData.Donations 
GROUP BY email2, first, last) As b

ON a.email1=b.email2 AND a.firstname=b.first AND a.lastname=b.last

在您的原始查询中，a 只是 BensData.Donations 的别名，因此您只能联接该表中存在的字段。