假设我们有这些表：
事件
id | name | time | action | entered
---+-------+-----------+--------+--------
1 | james | today | x |
1 | james | today | x | yes
1 | james | today | y |
1 | james | today | y | yes
2 | carl | today | x |
2 | carl | today | y |
3 | casey | yesterday | x |
3 | casey | yesterday | x | yes
3 | casey | yesterday | y |
3 | casey | yesterday | y | yes
4 | john | today | x | yes
用户
name | email |
------+--------------+
james | james@email |
casey | casey@email |
我是否可以创建 视图 ，从而产生以下内容？：
EventsView
id | name | time | action | entered
---+-------------+-----------+--------+--------
1 | james@email | today | x |
1 | james@email | today | x | yes
1 | james@email | today | y |
1 | james@email | today | y | yes
2 | carl | today | x |
2 | carl | today | y |
3 | casey@email | yesterday | x |
3 | casey@email | yesterday | x | yes
3 | casey@email | yesterday | y |
3 | casey@email | yesterday | y | yes
4 | john | today | x | yes
也就是说，我希望看到我有电子邮件的用户名，作为电子邮件，而不是名称本身。可能的？
答案 0 :(得分：1)
实现此目的的一种方法是使用coalesce以及select
e.id, coalesce(u.email, e.name) name, e.time, e.action, e.entered
from events e
left join users u on e.name = u.name
函数，该函数将返回其参数的第一个非null值。像这样：
axis.text.y = element_text(color = ...)