Re: Bypassing NULL elements in row_to_json function

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От David G. Johnston
Тема Re: Bypassing NULL elements in row_to_json function
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Msg-id CAKFQuwaL02r9RfYPfZD0rTZN=qQ0VFCBwjUthYeqhbWf0rWkTw@mail.gmail.com
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Ответ на Re: Bypassing NULL elements in row_to_json function  (Raymond O'Donnell <rod@iol.ie>)
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On Fri, Apr 8, 2016 at 8:53 AM, Raymond O'Donnell <rod@iol.ie> wrote:
On 08/04/2016 16:31, Michael Nolan wrote:
> I'm looking at the possibility of using JSON as a data exchange format
> with some apps running on both PCs and Macs.   .
>
> The table I would be exporting has a lot of NULL values in it.  Is
> there any way to skip the NULL values in the row_to_json function and
> include only the fields that are non-null?

You could use a CTE to filter out the nulls (not tested - I haven't used
JSON in PG (yet!)):

with no_nulls as (
  select ... from my_table
  where whatever is not null
)
select row_to_json(....) from no_nulls;

​One of us is confused.  I'm reading this as "I want a row_to_json" call to generate objects with different keys depending on whether a given key would have a null - in which case exclude the key.

I
​ think one would have to simply allow row_to_json to populate the keys with null values and then post-process them away:

json_strip_nulls(row_to_json(...))​


David J.

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