mysql - 从表中选择行但尽可能检索覆盖

Question

给定表格:

id    domain        name    value
----------------------------------
1     NULL          a       v1
2     example.com   a       v2
3     example.net   a       v3
4     NULL          b       v4
5     example.net   b       v5
6     example.com   c       v6
7     example.com   d       v7
8     NULL          d       v8

如何运行一个查询来检索域 =“example.com”的以下结果？请注意，当未为域指定值时，假定为 NULL 域。

name    value
--------------
a       v2
b       v4
c       v6
d       v7

对于域 = "example.net":

name    value
--------------
a       v3
b       v5
d       v8

Answer 1

像这样

(select name, value
from <your_table_name>
where domain = 'example.com')
union
(select name, value
from <your_table_name>
where domain is null
and name not in
    (select name
    from <your_table_name>
    where domain = 'example.com'))