AVG沒有給出正確的值 - Postgresql

Question

我有一個表，其中有很多冗餘點，我想選擇不同的點使用（不同），並選擇一些行的平均值（如rscp）。 我們這裏有一個例子：

| id | point     | rscp | ci 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 
| 1 | POINT(10.1192 36.8018) | 10  | 701 
| 2 | POINT(10.1192 36.8018) | 11  | 701 
| 3 | POINT(10.1192 36.8018) | 12  | 701 
| 4 | POINT(10.4195 36.0017) | 30  | 701 
| 5 | POINT(10.4195 36.0017) | 44  | 701 
| 6 | POINT(10.4195 36.0017) | 55  | 701 
| 7 | POINT(10.9197 36.3014) | 20  | 701 
| 8 | POINT(10.9197 36.3014) | 22  | 701 
| 9 | POINT(10.9197 36.3014) | 25  | 701 

什麼，我想是這樣的表如下：（rscp_avg是冗餘點的RSCP的平均值）

| id | point     | rscp_avg | ci 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 
| * | POINT(10.1192 36.8018) | 11   | * 
| * | POINT(10.4195 36.0017) | 43   | * 
| * | POINT(10.9197 36.3014) | 22.33  | * 

---

我想這一點，但它給了我一個錯誤的平均值！

select distinct on(point) 
id,st_astext(point),avg(rscp) as rscp_avg,ci 
from mesures 
group by id,point,ci; 

感謝您的幫助(^_^)

Answer 1

Hamdoulah！感謝上帝 ！

我剛纔找到解決辦法：

select on distinct(point) 
id,st_astext(point),rscp_avg,ci 
from 
(select id,point,avg(rscp) over w as rscp_avg,ci 
from mesures 
window w as (partition by point order by id desc) 
) ss 
order by point,id asc; 

，幫助我的網站是：

http://www.postgresql.org/docs/9.1/static/tutorial-window.html

http://www.w3resource.com/PostgreSQL/postgresql-avg-function.php