Re: add function argument name to substring and substr - Mailing list pgsql-hackers
| From | David G. Johnston |
|---|---|
| Subject | Re: add function argument name to substring and substr |
| Date | |
| Msg-id | CAKFQuwZ=ZEkQaFZBRpukNn-qvk4U52ZAsrLLRPAC4hgcZsJmkQ@mail.gmail.com Whole thread Raw |
| In response to | Re: add function argument name to substring and substr (jian he <jian.universality@gmail.com>) |
| Responses |
Re: add function argument name to substring and substr
|
| List | pgsql-hackers |
On Mon, Mar 17, 2025 at 8:20 PM jian he <jian.universality@gmail.com> wrote:
On Tue, Feb 18, 2025 at 6:13 AM David G. Johnston
<david.g.johnston@gmail.com> wrote:
>
> Table 9.9 limits itself to those functions defined in the SQL standard; which are basically the ones that use keywords instead of commas.
>
> The substring(string, start, count) function you note is already covered in Table 9.10 but we spell it substr(...)
>
> I don't think adding yet more spellings of this same function is warranted or desirable at this point.
ok.
> I'd maybe add a note if substring(,,,) works to substr saying that substring is a valid alias. I could be convinced to just document though.
>
it seems already in the doc.
substr ( string text, start integer [, count integer ] ) → text
Extracts the substring of string starting at the start'th character,
and extending for count characters if that is specified. (Same as
substring(string from start for count).)
substr ( bytes bytea, start integer [, count integer ] ) → bytea
Extracts the substring of bytes starting at the start'th byte, and
extending for count bytes if that is specified. (Same as
substring(bytes from start for count).)
new patch attached.
main changes:
1. change 3 argument func argument from
(string text, pattern text, escape_character text)
to
(string text, pattern text, escape text)
Why? It can only be one character so that existing name seems well chosen.
postgres=# select substring('123^^,123',',','^^');
ERROR: invalid escape string
HINT: Escape string must be empty or one character.
CONTEXT: SQL function "substring" statement 1
ERROR: invalid escape string
HINT: Escape string must be empty or one character.
CONTEXT: SQL function "substring" statement 1
2. add synopsis section in 9.7.3. POSIX Regular Expressions for
function substring.
we only have the synopsis section for function substring in 9.7.2
section, now add it to 9.7.3.
I'd probably try and resolve that the other way...point the reader to the reference page for the function if they want to see syntax. I'm mixed on (leaning against) whether choosing this place to demonstrate all the possible spellings is the best.
also add an example about using named natation call substring:
substring(string=>'foobar', pattern=> 'o.b')
I'm already pulling my hair out at this showing all the insanity that exists without adding this to the mix.
The vast majority of examples throughout the manual use traditional function call syntax func_name(arg1, arg2, etc.); I'd rather keep with convention than start to scatter about alternative syntax choices just to give the random reader who happens upon this fairly esoteric part of the manual the benefit of seeing their options. If that is a goal, then I'd suggest spending some time in our Tutorial adding some more examples with these alternative forms to people looking to be exposed to new things in the place they'd go to look for them. They probably won't learn about them from the Syntax section.
substring(string text, pattern text[, escape-character text])
to Table 9.10
I'd also rename escape to escape-character in the other SQL substring function synopses. The RegEx page got that part correct.
Do as little or as much with the RegEx section as you'd like, though it seems like separate material from $subject. The page seems to already use replaceable names instead of data types so on that score it should be unaffected if we've chosen the same names.
Food for thought, it seems a bit redundant to name the first argument basically the same as the data type. I was thinking that "content" would be a better choice. This is basically a polymorphic function where all the inputs are the same thing just having different types - and that thing is being "content".
David J.
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