On Sunday, December 10, 2023, PG Bug reporting form <
noreply@postgresql.org> wrote:
The following bug has been logged on the website:
Bug reference: 18239
Logged by: Luc Van Linden
Email address: lucvanlind.en@gmail.com
PostgreSQL version: 15.3
Operating system: windows 10 64 bit
Description:
We simplified the bug, or maybe undocumented behavior to its simplest
testcase.
select position ('' in 'A') returns 1
Thus, case a field has an empty string while, checking positions in another
string, it seems to always fit the position 1.
Not sure if this is intended or not, at least we experience this as a bug.
Just as an empty set is a subset of all sets the empty string is a substring within all strings.
I do not believe we document or refer to this external rule anywhere though.
David J.