在JOIN的ON子句中使用別名

Question

堆棧溢出的新功能（通常是編碼）。

我做了一些研究，但是找不到以下問題的答案：

如何在應用於維的函數結果上而不是維本身上聯接兩個表？

即我想在函數lower（）的小寫結果上聯接以下兩個表，而不是在大小寫不明確的維度上聯接。

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

它不允許我加入在第一個表（a）中創建的別名，但是，如果我加入表a中的原始維度（first_name和last_name），則結果基於大小寫不明確的維度，並給出不良結果。

我希望這很清楚。

謝謝你的幫助！

Answer 1

嘗試使用兩個子查詢，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

在原始查詢中，a只是BensData.Donations的別名，因此您只能聯接該表中存在的字段。

Answer 2

我從未聽說過join each ，也沒有將其記錄為MySQL連接的語法（請參見此處）。

試試這個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

您的版本在列之間的子查詢中也缺少逗號。

為了清楚起見，您可能應該將from子句寫為：

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

或從子查詢中刪除lower() 。 否則，您將依賴於服務器，數據庫和表的默認歸類來確定on子句的實際作用。

Answer 3

感謝大家的幫助！

特別扣人心弦的人向我指出了正確的方向！ 他的代碼和我的代碼的主要區別在於，我的代碼沒有在第一個SELECT子句的每個維的前面附加表別名（例如** a。** fistname，** a。** lastname，- ->名字，姓氏）

由於某種原因，BigQuery一直由於表別名而給我一個錯誤。

這是起作用的代碼。

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

感謝你的幫助！