<sup>I posted the same <strike>[question][1] on stackoverflow</strike> (now deleted), but did not get an answer.  
Perhaps this would be a better forum to ask it.</sup>

Following the [answer][2] to this [question][3], I have managed to produce the following output to get a running count of values:

    id      creation                    operation       value       running sum
    SyJw-c  2016-09-01 00:11:08.307419  positive_op_1   1.33        28.82
    SyJw-c  2016-08-21 08:32:54.431662  negative_op_1   -1          27.49
    SyJw-c  2016-08-18 07:38:33.878365  positive_op_2   1           28.49
    SyJw-c  2016-08-14 18:12:03.599797  negative_op_1   -1          27.49
    SyJw-c  2016-08-02 15:44:29.693303  positive_op_1   1.33        28.49
    SyJw-c  2016-07-31 12:08:50.659905  override_op_1   4.66        27.16
    SyJw-c  2016-06-26 06:53:54.537603  negative_op_1   -3.5        22.5
    SyJw-c  2016-05-31 13:34:08.005687  negative_op_1   -1          26
    SyJw-c  2016-05-31 13:34:04.776970  negative_op_1   -1          27
    SyJw-c  2016-05-31 11:27:09.502983  override_op_2   28          28

***BUT*** my case is more complex. Not only do I need to sum up the values, I need to be able to perform a conversion first to some rows based on the running sum of the row right beneath it.

Let me first explain the motivation:

Currently I have a table with incremental, decremental and override operations. I would like to port the data to a table with only incremental and decremental operations such that I would be able to straightforwardly sum up the values. I am not looking to maintain the old table, simply a way to migrate the data into a simpler model and henceforward to append data to the new table only.

Taken the "raw" table above, I would like to write a query (I am running on postgresql 9.5) and get a table as closely resembling the below. (**Conversely, I would like to know that what I am attempting is *impossible***)

Note the override operators are interspersed between the normal operators, they may appear more than twice as in the example, also, all initial operators (the earliest in the table) are override with an initial value that should be taken into account as in the example below. Moreover I had shown only data belonging to one group (same id) but the general idea is to perform this migration for all groups. Lastly I show the math in parentheses, I don't need that in the result, it is for the example only:

    id      creation    oper      transformed_op   value   transformed_value       running sum
    SyJw-c  2016- ...  pos_op_1                    1.33    1.33                    10.98
    SyJw-c  2016- ...  neg_op_1                    -1      -1                      9.65
    SyJw-c  2016- ...  pos_op_2                    1       1                       10.65
    SyJw-c  2016- ...  neg_op_1                    -1      -1                      9.65
    SyJw-c  2016- ...  pos_op_1                    1.33    1.33                    10.65
    SyJw-c  2016- ...  ovr_op_1   new_rel_op_1     4.66    (4.66-22.5) = -17.84    4.66
    SyJw-c  2016- ...  neg_op_1                    -3.5    -3.5                    22.5
    SyJw-c  2016- ...  neg_op_1                    -1      -1                      26
    SyJw-c  2016- ...  neg_op_1                    -1      -1                      27
    SyJw-c  2016- ...  ovr_op_2   new_rel_op_2     28      (28-0) = 28             28


  [1]: http://stackoverflow.com/q/39367751/101715
  [2]: http://stackoverflow.com/a/22843199/101715
  [3]: http://stackoverflow.com/questions/22841206/calculating-cumulative-sum-in-postgresql