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From: Dian Fay <[email protected]>
To: jian he <[email protected]>
To: Peter Eisentraut <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: add function argument names to regex* functions.
Date: Mon, 01 Jan 2024 13:05:45 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CACJufxHeyc34PMx6OnWb-xoaMtj1Yoax1rM+71zkwCynvmVwdg@mail.gmail.com>
References: <CACJufxG3NFKKsh6x4fRLv8h3V-HvN4W5dA=zNKMxsNcDwOKang@mail.gmail.com>
	<[email protected]>
	<CACJufxHeyc34PMx6OnWb-xoaMtj1Yoax1rM+71zkwCynvmVwdg@mail.gmail.com>

On Wed Dec 27, 2023 at 10:28 PM EST, jian he wrote:
> On Thu, Dec 28, 2023 at 6:25 AM Peter Eisentraut <[email protected]> wrote:
> >
> > On 27.12.23 17:53, jian he wrote:
> > > similar to [1], add function argument names to the following functions:
> > > regexp_like, regexp_match,regexp_matches,regexp_replace,
> > > regexp_substr,regexp_split_to_array,regexp_split_to_table,regexp_count
> >
> > Note that these functions are a quasi-standard that is shared with other
> > SQL implementations.  It might be worth looking around if there are
> > already other implementations of this idea.
> >
>
> turns out people do like calling functions via explicitly mentioning
> function argument names, example: [0]
> There are no provisions for the argument names.
>
> I looked around the oracle implementation in [1], and the oracle regex
> related function argumentation name in [2]
> I use the doc [3] syntax explanation and add the related function names.
>
> Current, regex.* function syntax seems fine. but only parameter `N`
> seems a little bit weird.
> If we change the function's argument name, we also need to change
> function syntax explanation in the doc; vise versa.
>
> QUOTE:
> The regexp_instr function returns the starting or ending position of
> the N'th match of a POSIX regular expression pattern to a string, or
> zero if there is no such match. It has the syntax regexp_instr(string,
> pattern [, start [, N [, endoption [, flags [, subexpr ]]]]]). pattern
> is searched for in string, normally from the beginning of the string,
> but if the start parameter is provided then beginning from that
> character index. If N is specified then the N'th match of the pattern
> is located, otherwise the first match is located.
> END OF QUOTE.
>
> maybe we can change `N` to occurrence. but `occurrence` is kind of verbose.
>
> [0] https://stackoverflow.com/questions/33387348/oracle-named-parameters-in-regular-functions
> [1] https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/REGEXP_SUBSTR.html#GUID-2903904D...
> [2] https://dbfiddle.uk/h_SBDEKi
> [3] https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP

I've been trying to use named arguments more diligently so expanding
support for built-in functions is welcome. The patch applies cleanly and
works as advertised.

I agree that the parameter name `n` is not ideal. For example, in
`regexp_replace` it's easy to misinterpret it as "make up to n
replacements". This has not been a problem when `n` only lives in the
documentation which explains exactly what it does, but that context is
not readily available in code expressing `n => 3`.

Another possibility is `index`, which is relatively short and not a
reserved keyword ^1. `position` is not as precise but would avoid the
conceptual overloading of ordinary indices.

1. https://www.postgresql.org/docs/current/sql-keywords-appendix.html

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