SQL-使用有序组的前N行的SUM创建视图

Question

I've this table in my MYSQL db, and I want to create a view as the title. Table:

ID | Result
---+-------
1  | 10
3  | 7
1  | 4
2  | 5
1  | 3

The view should select group by ID, SUM(result), and consider only the best 2 results for each ID, and order everything by the result. So.. View:

ID | Result
---+--------
1  | 14
3  | 7
2  | 5

I tried with:

CREATE OR REPLACE VIEW final_res AS 
SELECT  `ID` , SUM(  `result` ) 
FROM  `result_table`
GROUP BY  `ID`
HAVING COUNT(*)<=2
ORDER BY `result`

But this doesn't work. :/

Answer 1

One option is to create a row number using user-defined variables within each group ordered by the result desc , and then limit the sum to the first 2 rows within each group:

select id, sum(result)
from (
  select id, result, @rn:=if(@prevId=ID,@rn+1,1) rn, @prevId:=id
  from result_table join (select @rn:=0, @previd:=0) t
  order by id, result desc
  ) t
where rn <= 2
group by id
order by 2 desc

• SQL Fiddle Demo

---

Alternatively, you could use a correlated subquery, but I think the row number approach is a bit cleaner:

select t.id, max(t.result) + coalesce((
  select max(t2.result)
  from result_table t2 
  where t.id = t2.id and t.result != t2.result
  ),0)
from result_table t
group by id
order by 2 desc

• Additional Fiddle

Answer 2

You're not going to get anything because you're grouping on ID, your HAVING clause is saying where there's more than one ID. This will never happen

CREATE OR REPLACE VIEW final_res AS 
SELECT TOP 2 `ID` , SUM(  `result` ) 
FROM  `result_table`
GROUP BY  `ID`
ORDER BY `result` desc