Re: split_part for the last element

From: Nikhil Benesch <nikhil(dot)benesch(at)gmail(dot)com>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: "pgsql-generallists(dot)postgresql(dot)org" <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: Re: split_part for the last element
Date: 2020-10-23 18:38:26
Message-ID: CAPWqQZQyU35LH+PBqb8jWS94GRHUivToVFgqi=AndBP1AySSYA@mail.gmail.com
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On Fri, Oct 23, 2020 at 2:21 PM David G. Johnston
<david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> I'm torn here because this would be the first usage of this concept in
> PostgreSQL (I think).

Yeah, I also have some qualms about this design in the context of Postgres.
Particularly because Postgres allows arrays to begin at negative indices.

> Tangentially, I noticed that we have a "starts_with" function but no
> corresponding "end_with".

Ah, interesting. On the other hand, there are both "left" and "right",
"lpad" and "rpad", and "ltrim" and "rtrim". And at least ends_with has the
fairly elegant alternative of "s LIKE '%suffix'".

> It's been a while but there used to be a systemic inertia working against
> adding minor useful functions such as these.
>
> With the new documentation layout I would at least consider updating the
> description for the normal functions with an example on how to formulate
> an expression that works contra-normally, and in the case where there does
> exist such a specialized function, naming it.

Supposing you go this route, which of the options would you envision
mentioning as the converse of split_part?

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