mysql - 选择不同但具有列的值

Question

这就是我想要的。

假设我们有这张表

Name  Email          Department             Branch
------------------------------------------------------
John  john@test.ca   Information Technology SAP
John  john@test.ca   Not Available          Not Available
Bret  brett@test.ca  Emergency Response     911
Bret  brett@test.ca  Not Available          Not Available
diana diana@test.ca  Not Available          Not Available

现在我基本上想要的是得到以下结果:

如果约翰有“信息技术”和“不可用”，则“信息技术”将成为优先级。基本上，如果约翰不属于任何其他部门，它只会显示“不可用”行。所以结果表将是这样的:

Name  Email         Department             Branch
-----------------------------------------------------
John  john@test.ca  Information Technology SAP
Bret  brett@test.ca Emergency Response     911
Diana diana@test.ca Not Available          Not Available

谢谢!

Answer 1

对于此示例数据，您需要一个 CASE 表达式来检查 'Not available' 并将其视为 NULL，以便您可以聚合 (与 MIN 或 MAX):

select name, email,
  coalesce(
    max(case when department = 'Not Available' then null else department end),
    'Not Available'
  ) department,
  coalesce(
    max(case when branch = 'Not Available' then null else branch end),
    'Not Available'
  ) branch
from tablename
group by name, email

请参阅demo .
结果:

| name  | email         | department             | branch        |
| ----- | ------------- | ---------------------- | ------------- |
| Bret  | brett@test.ca | Emergency Response     | 911           |
| diana | diana@test.ca | Not Available          | Not Available |
| John  | john@test.ca  | Information Technology | SAP           |