如何计算成本平均值，postgresql 9.5+

Question

我的环境是postgresql 9.5 +

如果可能，我想用窗口函数计算成本平均值

例如

kdproduk  code  tgl           qty   harga   totalharga
abc         2   2016-10-20     5    10000   50000
abc         4   2016-10-21    -3    12000   36000   
abc         2   2016-10-22    10    13000   130000  

然后我的查询是：

with ab as (   
  SELECT
      kdproduk,
      code,
      tgl,
      qty,
      harga,
      totalharga,
      coalesce(hargarata2, 0) as hargarata2,
      sum(qty) OVER (PARTITION BY kdproduk ORDER BY kdproduk, tgl, code) AS running_qty
    FROM ms_kartustok
    ORDER BY kdproduk, tgl, code )

select   kdproduk, code, tgl,   qty, harga, totalharga,   coalesce(running_qty, 0) + qty as running_qty,   case
    when code = 2 then (totalharga + coalesce(hargarata2, 0)) / (coalesce(running_qty, 0) + qty)
    else hargarata2   end as rata2 from   (
    SELECT
      kdproduk,
      code,
      tgl,
      qty,
      harga,
      totalharga,
      lag(hargarata2) OVER (PARTITION BY kdproduk ORDER BY kdproduk, tgl, code) AS hargarata2,
      lag(running_qty) OVER (PARTITION BY kdproduk ORDER BY kdproduk, tgl, code) AS running_qty
    FROM ab
    ORDER BY kdproduk, tgl, code   ) as a

我的查询结果是：

kdproduk  code  tgl           qty   harga   totalharga  running_qty   rata2
abc         2   2016-10-20     5    10000   50000       5             10000
abc         4   2016-10-21    -3    12000   36000       2             0
abc         2   2016-10-22    10    13000   130000      12            10833.333333333334

但我希望结果是：

kdproduk  code  tgl           qty   harga   totalharga  running_qty   rata2
abc         2   2016-10-20     5    10000   50000       5             10000
abc         4   2016-10-21    -3    12000   36000       #2#         #10000#
abc         2   2016-10-22    10    13000   #130000#    12            12500

如果＆＃34;代码＆＃34;是4，然后是我的专栏＆＃34; rata2＆＃34;是以前＆＃34; rata2＆＃34;值。 如果＆＃34;代码＆＃34;是2，那么我的专栏＆＃34; rata2＆＃34;价值是： （totalharga +＆＃34;＆＃34之前的rata2值;）/（qty +＆＃34;＆＃34之前的running_qty值;）

第3行是：

(130000 + (2*10000)) / (10 + 2) = 12500

编辑： 看到上面的表格，我使用符号＃

如何解决这个问题？

感谢。