Re: BUG #18765: Inconsistent behaviour and errors with LIKE

On Fri, Jan 3, 2025 at 10:04 AM PG Bug reporting form <
noreply(at)postgresql(dot)org> wrote:

> The following bug has been logged on the website:
>
> Bug reference: 18765
> Logged by: Anmol Mohanty
> Email address: anmol(dot)mohanty(at)salesforce(dot)com
> PostgreSQL version: 17.0
> Operating system: NA(used fiddle tool at sqlfiddle.com)
> Description:
>
> select 'a\' like 'a\'; -- error - LIKE pattern must not end with escape
> character
> select 'a' like 'a\'; -- f - query runs
> This doesn't make sense. The LIKE pattern is incorrect in both.
>
> I've also checked around constant folding and runtime non-literal values by
> inserting into cte's and temp tables. Same outcome.
>
> ```
> WITH a AS (SELECT 'xyz' AS value)
> SELECT value LIKE 'xyz\' AS result
> FROM a;
> ```
> f
>
>
Working as designed.

Execution optimization combined with non-compilation.

You may not get a failure if the condition is proven to evaluate to false
before encountering the malformed part of the expression. There is no
compilation step that evaluates the supplied text for correctness
independent of its usage. The input string running out of characters while
the test string still has some is known to result in a false outcome.

David J.