Google bigquery 键为空时Bigquery合并联接

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   |
+---------+-----------+--------+

我想基于t1.user\u id=t2.user\u id加入，但当密钥为空时，请在t1.email=t2.email上加入

我尝试了多种方式加入bigquery，如下所示：
1.）合并时（t1.用户id，t1.电子邮件）=合并时（t2.用户id，t2.电子邮件）
2.）在t2.user_id不为null的情况下，则t1.user_id=t2.user_id else t1.email=t2.email结束

---

两者都不起作用。如何做到这一点？

我会将这样的连接拆分为两个单独的：
第一个-按用户\u id加入

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

第二-通过电子邮件加入第一次加入中丢失的ID

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

---

谢谢我真的希望它能使用联合。基于链接，这似乎是可能的。但是，我想BigQuery不支持吗？per:join\u谓词：field\u from\u one\u side\u of \u the \u join=field\u from\u the \u other\u side\u of \u of \u the \u join[AND…]SQL有“IS DISTINCT”和“IS NOT DISTINCT”，但我在BigQuery中看不到这一点。