如何从具有不同条件的同一张表中获取行

Question

我想从具有不同条件的同一张表中获取数据。我在 android studio 中使用 sqlite。

**ID    Name       Role**
1   Emma       Manager
2   Olivia     Manager
3   Ava        Manager
4   Isabella   Sales officer
5   Sophia     Sales Officer
6   Charlotte  Sales Officer
7   Mia        Clerk
8   Amelia     Clerk

假设这张表，我有不同类型的角色和不同数量的角色。我想从每个角色中选择 2 个人。

Select * from employeeTable where role = 'Manager' LIMIT 2
Select * from employeeTable where role = 'Sales officer' LIMIT 2
Select * from employeeTable where role = 'Clerk' LIMIT 2

我只是想加入这三个查询的结果。 对不起，如果这个幼稚的问题。并提前感谢

Answer 1

带有row_number()窗口功能：

select t.id, t.name, t.role 
from (
  select *, row_number() over (partition by role) rn
  from employeeTable
) t
where t.rn <= 2

你也可以定义：

partition by role order by name

或：

partition by role order by id

而不仅仅是：

partition by role

获取结果中的特定行。
请参阅demo。
结果：

| ID  | Name     | Role          |
| --- | -------- | ------------- |
| 7   | Mia      | Clerk         |
| 8   | Amelia   | Clerk         |
| 1   | Emma     | Manager       |
| 2   | Olivia   | Manager       |
| 4   | Isabella | Sales Officer |
| 5   | Sophia   | Sales Officer |

Answer 2

尝试查询并检查是否有效：

Select * from employeeTable where role = 'Manager' LIMIT 2
UNION ALL
Select * from employeeTable where role = 'Sales officer' LIMIT 2
UNION ALL
Select * from employeeTable where role = 'Clerk' LIMIT 2