BIGQUERY合併加入時密鑰爲空

Question

表1

+---------+-----------+--------+ 
| user_id | email  | action | 
+---------+-----------+--------+ 
| 1  | aa@aa.com | open | 
+---------+-----------+--------+ 
| 2  | null  | click | 
+---------+-----------+--------+ 
| 3  | ac@ac.com | click | 
+---------+-----------+--------+ 
| 4  | ad@ad.com | open | 
+---------+-----------+--------+ 

表2

+---------+-----------+--------+ 
| user_id | email  | event | 
+---------+-----------+--------+ 
| 1  | aa@aa.com | sent | 
+---------+-----------+--------+ 
| null | ac@ac.com | none | 
+---------+-----------+--------+ 
| 2  | ab@ab.com | sent | 
+---------+-----------+--------+ 
| 4  | ad@ad.com | sent | 
+---------+-----------+--------+ 

我想根據加入t1.user_id = t2.user_id，但是當有一個空的鍵，加入上t1.email = t2.email

我嘗試多種方式在BigQuery中加入如：
1）ON COALESCE（t1.user_id，t1.email）= COALESCE（t2.user_id，T2。電子郵件）
2.）ON在t2.user_id不爲空的情況下，則t1.user_id = t2.user_id else t1.email = t2.email end

兩者都不工作。如何才能做到這一點？

Answer 1

我會分流，加入到兩個獨立的：
首先 - 由USER_ID加入

SELECT * 
FROM table1 AS t1 
JOIN table2 AS t2 
ON t1.user_id = t2.user_id 

二 - 通過電子郵件參加了在懷念那些IDS首次加入

SELECT * 
FROM (
    SELECT * FROM table1 
    WHERE user_id NOT IN (
    SELECT t1.user_id 
    FROM table1 AS t1 
    JOIN table2 AS t2 
    ON t1.user_id = t2.user_id 
) 
) t1 
JOIN (
    SELECT * FROM table2 
    WHERE user_id NOT IN (
    SELECT t1.user_id 
    FROM table1 AS t1 
    JOIN table2 AS t2 
    ON t1.user_id = t2.user_id 
) 
) t2 
ON t1.email = t2.email