title: How to chose the previous non null value in a column for null values resulting from an outer join
body: <p>Say I have a table A, which has null values in a particular column say Value as a result of an outer join. Now if A represents a value such as cumsum, it doesnt make sense for it to drop to null in the middle</p>
  <pre><code>| ID  | Value |
  | --- | ----- |
  | 1   | null  |
  | 2   | 576   |
  | 3   | null  |
  | 4   | 695   |
  | 5   | null  |
  </code></pre>
  <p>so is it possible to transform the table A, to table B which might look like this</p>
  <pre><code>| ID  | Value |
  | --- | ----- |
  | 1   | 0     |
  | 2   | 576   |
  | 3   | 576   |
  | 4   | 695   |
  | 5   | 695   |
  </code></pre>
  <p>Therefore is it possible to replace the null values in a column with either the previous non null value, or if in case that is not available a default value 0.
  This transformation also has to be done across all columns in a table, with 10 or so columns.</p>