Re: BUG #15805: Problem with lower function for greek sigma (Σ) letter

> On 15 May 2019, at 09:57, PG Bug reporting form <noreply(at)postgresql(dot)org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference: 15805
> Logged by: Sergey kuznetsov
> Email address: iksss(dot)88(at)gmail(dot)com
> PostgreSQL version: 9.6.10
> Operating system: linux
> Description:
>
> I see unexpected behaviour of lower function for greek sigma letter Σ.
> According to wikipedia (https://en.wikipedia.org/wiki/Sigma) if this letter
> is in final word position, it should be ς in lowercase, and not σ. But
> PotgreSQL lower function returns σ, for example lower('ΔΗΜΟΤΕΣ ΦΑΙΣΤΟΥ') =
> "δημοτεσ φαιστου" instead of "δημοτες φαιστου". So if I try to pass this
> lower string from another part of a system (java code, for example) Postgre
> will not return this row cause it differs from java-generated one.

This is indeed a bug, and a rare occurrence since AFAICT from ISO 30112 and
googling there is only a single case of word-final lowercasing which is this
sigma. The attached patch takes a stab at fixing this.

cheers ./daniel