Horton

Re: strpos behavior change around empty substring in PG12

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Shay Rojansky <roji@roji.org>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-10-28T15:48:49Z
Lists: pgsql-hackers 
On Mon, Oct 28, 2019 at 11:02 AM Shay Rojansky <roji@roji.org> wrote:
> Before PG12, select strpos('test', '') returns 1 (empty substring found at first position of the string), whereas starting with PG12 it returns 0 (empty substring not found).
>
> Is this behavior change intentional? If so, it doesn't seem to be documented in the release notes...
>
> First raised by Austin Drenski in https://github.com/npgsql/efcore.pg/pull/1068#issuecomment-546795826

It looks to me like this got broken here:

commit 9556aa01c69a26ca726d8dda8e395acc7c1e30fc
Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:   Fri Jan 25 16:25:05 2019 +0200

    Use single-byte Boyer-Moore-Horspool search even with multibyte encodings.

Not sure what happened exactly.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Handle empty-string edge cases correctly in strpos().

  2. Use single-byte Boyer-Moore-Horspool search even with multibyte encodings.