在 JOIN 的 ON 子句中使用别名

Question

Stack Overflow 的新手（以及一般的编码）。

我做了一些研究，但无法找到以下问题的答案：

如何将两个表格连接到应用于维度的函数结果，而不是维度本身？

即我想将以下两个表加入函数 lower() 的小写结果，而不是加入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

它不允许我加入我在第一个表 (a) 中创建的别名，但是，如果我加入表 a 中的原始维度（first_name 和 last_name），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。

我希望这很清楚。

感谢您的帮助！

Answer 1

感谢大家的帮助！

尤其是 sprocket，他为我指明了正确的方向！他的代码和我的主要区别在于我的代码没有在第一个 SELECT 子句的每个维度的前面附加表别名（例如 **a.**fistname, **a.**lastname, --- --> 名，姓）

由于表别名，BigQuery 一直给我一个错误。

这是有效的代码。

SELECT
firstname
,lastname
,email1
,total_donated
FROM

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

JOIN EACH

(Select
lower(first_name) as first
,lower(last_name) as last
,lower(email) as email2
,sum(float(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

感谢大家的帮助！

Answer 2

尝试使用两个这样的子查询：

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，因此您只能加入该表中存在的字段。

Answer 3

我从未听说过join each，并且它没有被记录为 MySQL 连接的语法（请参阅此处）。

试试这个from 子句：

From BensData.Donations a JOIN
     (Select lower(first_name) as first, lower(last_name) as last,
             sum(amount) as total_donated
      From BensData.Donations 
      GROUP BY first, last
     ) b
     ON a.firstname = b.first AND a.lastname = b.last

您的版本在列之间的子查询中也缺少逗号。

为清楚起见，您可能应该将from 子句写为：

     ON lower(a.firstname) = b.first AND lower(a.lastname) = b.last

或从子查询中删除lower()。否则，on 子句的实际作用取决于服务器、数据库和表的默认排序规则。