Re: [GENERAL] Desired behavior for || (jsonb_concat)

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От David G. Johnston
Тема Re: [GENERAL] Desired behavior for || (jsonb_concat)
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Msg-id CAKFQuwZtmAuySTp=oxk-WTXXQP+DS6MZQSxpK3ar8meRhYb6ZA@mail.gmail.com
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Ответ на [GENERAL] Desired behavior for || (jsonb_concat)  (Seamus Abshere <seamus@abshere.net>)
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On Thu, Jul 6, 2017 at 3:25 PM, Seamus Abshere <seamus@abshere.net> wrote:
hi,

# select '{"a":1}'::jsonb || null;
 ?column?
----------
 null
(1 row)

Is there a theoretical reason that this has to return null as opposed to
just {"a":1}?


Most operators in SQL, when given a null as an operand, output null.  Many of the underlying functions likewise are defined to be STRICT.  At this point its fair to say its a long-standing convention.

Aggregation of a null has mixed results as to whether the null is processed or ignored - the later typically in the math aggregations.

The following is a relatively easy work around for those who must handle the possibility of nulls in their data.

​select '{"a":1}'::jsonb || COALESCE(null, '{}')::jsonb;
​
While most such expressions could be seen to have an obvious default behavior when dealing with null SQL generally forces the user to make an explicit declaration of intent and falls back to "unknown" if that is not done.

David J.

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