如何获得每年SQLite的x最佳结果

Question

我的解决方案有问题，我找到了这个例子：

(SELECT COUNT(*) FROM person AS b    
WHERE b.group = a.group AND b.age >= a.age) <= 2    
ORDER BY a.group ASC, a.age DESC

（来自：Get top n records for each group of grouped results）

但是我需要在一个旧列的基础上创建一个新列，因此我需要进行一些计算，当我尝试添加更多列时，我收到一条错误消息。如果我只是添加满足感，就可以了，例如：

(SELECT COUNT(*) FROM person AS b   
WHERE b.group = a.group AND b.age*100 >= a.age*100) <= 2   
ORDER BY a.group ASC, a.age DESC   

但是当我尝试重命名新列时，AS过多。

我也尝试使用UNION ALL，但是我的SQLite对（）不满意。这根本不适合我：

(   
  select *     
  from mytable    
  where `group` = 1   
  order by age desc   
  LIMIT 2   
)   
UNION ALL   
(   
  select *   
  from mytable    
  where `group` = 2   
  order by age desc   
  LIMIT 2   
)   

“结果：”（“附近：语法错误在第1行：（“

即使我在（）之前执行SELECT和FROM，我也收到错误消息。

(where `group` = 1   
  order by age desc   
  LIMIT 2)   

UNION ALL   

select * from mytable    
(where `group` = 2   
  order by age desc   
  LIMIT 2)   

“ WHERE”附近：语法错误

请有人能解释一下为什么吗？

Answer 1

此语法应该起作用：

select * 
from (
  select *     
  from mytable    
  where `group` = 1   
  order by age desc   
  LIMIT 2   
)   
UNION ALL   
select * 
from (   
  select *   
  from mytable    
  where `group` = 2   
  order by age desc   
  LIMIT 2   
);

但是您也可以使用ROW_NUMBER（）：

select t.`group`, t.age, ....<rest of the columns from mytable> 
from (
  select *, row_number() over (partition by `group` order by age desc) rn
  from mytable
  where `group` in (1, 2)
) t 
where t.rn <= 2