posrgresql：混淆運行列

Question

現在，類似的問題已經被問了幾次在這個論壇的共有，但是，我已經被計算在posrgresql (Version 9.4.2)表中的列的每月運行總和掙扎：

created_at   | points 
----------------------------- 
2015-12-10 12:26:34 | 199 
2016-01-10 12:26:34 | 199 
2016-02-10 12:26:34 | 199 
2016-03-10 12:26:34 | 500 
2016-03-10 12:26:39 | 199 

預期的結果是：

created_at   | sum 
----------------------------- 
2015-12-01   | 199 
2016-01-01   | 398 
2016-02-01   | 597 
2016-03-01   | 1296 

工作sql我到達，主要是通過試驗和錯誤讀取其他線程後，是：

SELECT 
    date_trunc('month',created_at)::date as month_created, 
    sum(sum(points)) 
OVER 
    (
     ORDER BY date_trunc('month',created_at)::date 
    ) 
FROM 
    point_histories 
GROUP BY 1 
ORDER BY 1 ASC 

我的困惑是爲什麼以下（我顯然是誤解）工作？

SELECT 
    month_created, 
    sum(points), 
    sum(sum(points)) 
OVER 
    (
     PARTITION BY month_created 
     ORDER BY created_at 
    ) 
    AS cum_amt 
FROM 
    (
     SELECT 
      *, 
      date_trunc('month', created_at)::date as month_created 
     FROM 
      point_histories 
    ) 
    as derivedTable 
ORDER BY created_at 
GROUP BY month_created 

上面提供了以下錯誤：

********* Error ********** 

ERROR: syntax error at or near "group" 
SQL state: 42601 
Character: 314 

如果我刪除GROUP BY條款，我得到：

********** Error ********** 

ERROR: column "derivedtable.month_created" must appear in the GROUP BY clause or be used in an aggregate function 
SQL state: 42803 
Character: 12 

Answer 1

IMO，order by子句應該完成查詢。

SELECT 
    month_created, 
    sum(points), 
    sum(sum(points)) 
OVER 
    (
     PARTITION BY month_created 
     ORDER BY created_at 
    ) 
    AS cum_amt 
FROM 
    (
     SELECT 
      *, 
      date_trunc('month', created_at)::date as month_created 
     FROM 
      point_histories 
    ) 
    as derivedTable 
GROUP BY month_created 
ORDER BY created_at