如何从GROUP BY中选择From Table

Question

我有一张表machine：

 - id: int
 - name: varchar (100)
 - mark: varchar (100)
 - price: double 

包含数据：

1, keyboard, mark1, 10
2, mouse, mark2, 15
3, keyboard, mark3, 50
4, computer, mark4, 120
5, mouse, mark5, 90 

我想显示具有按名称分组的机器列表，其中包含最后一个入门价格：

1(first), keyboard(first), mark1(first), 50(last)
2(first), mouse(first), mark2(first), 90(last)
4, computer, mark4, 120

• 价格50来自以下行：3，键盘，mark3,50
• 价格90来自该行：5，鼠标，mark5,90

我尝试了这个查询：

SELECT * FROM machine GROUP BY name 

但我没有任何想法让我看到我的结果。

Answer 1

SELECT name, MAX(price) FROM machine GROUP BY name

如果您还想选择标记，则需要对列进行分组或汇总

Answer 2

有一个子查询m2，它返回每台机器的最高ID（即具有最新价格的行）。使用m2加入m1以获得整行：

select m1.*
from machine m1
join (select name, max(id) as id from machine group by name) m2
  on m1.name = m2.name
  and m1.id = m2.id

可以简化为：

select m1.*
from machine m1
join (select max(id) as id from machine group by name) m2
  on m1.id = m2.id

Answer 3

[END]

Answer 4

应该做的伎俩

D:\Test\Info\TestProject.dll