Re: BUG #18451: NULL fails to coerce to string when performing string comparison

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От David G. Johnston
Тема Re: BUG #18451: NULL fails to coerce to string when performing string comparison
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Msg-id CAKFQuwZ0p7v7QOd_oH37P88dDUAV-wiRanE9K=6qsjG9QN+4tg@mail.gmail.com
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Ответ на BUG #18451: NULL fails to coerce to string when performing string comparison  (PG Bug reporting form <noreply@postgresql.org>)
Ответы Re: BUG #18451: NULL fails to coerce to string when performing string comparison
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On Monday, April 29, 2024, PG Bug reporting form <noreply@postgresql.org> wrote:
The following bug has been logged on the website:

Bug reference:      18451
Logged by:          Darryl Dixon
Email address:      darryl.dixon@gmail.com
PostgreSQL version: 14.11
Operating system:   Ubuntu 22.04 64Bit
Description:       

postdb=# select where 'ab' like '%a%';
--
(1 row)

postdb=# select where 'ab'||NULL like '%a%';
--
(0 rows)

postdb=# select where 'ab'||NULL::text like '%a%';
--
(0 rows)

You are mistaken in believing that concatenation involving null produces a non-null result.  It is rather an inherently “strict” operation.
 

postdb=# select where 'ab'||format('%s', NULL::text) like '%a%';
--
(1 row)

Whereas format() is not “strict” and you choice of %s results in the documented empty string substitution.

David J.

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