From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: string function - "format" function proposal |
Date: | 2010-08-30 16:08:54 |
Message-ID: | AANLkTikQ8RSBPTqAfW+1DWASVLsJjkXLKDh4zVMD3bN2@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
2010/8/30 Alvaro Herrera <alvherre(at)commandprompt(dot)com>:
> Excerpts from Pavel Stehule's message of lun ago 30 07:51:55 -0400 2010:
>> 2010/8/30 Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>:
>> > On Mon, Aug 30, 2010 at 7:58 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
>> >> propsals:
>> >> * "format" function - uses same formatting as PL/pgSQL RAISE statement
>> >> * "sprintf" function
>> >>
>> >> Now I propose a compromise - "format" function with only three tags:
>> >> %s .. some string
>> >> %i .. SQL identifier
>> >> %l .. string literal
>> >
>> > These are just ideas:
>> >
>> > * Use $n, as like as PREPARE command.
>> > It allows for us to swap arguments in any order.
>> > SELECT format('$2 before $1', 'aaa', 'bbb')
>>
>> what is use case for this feature? I don't see it.
>
> Translations :-) I haven't had a use for that but I've heard people
> implements gettext of sorts in database tables. Maybe that kind of
> thing would be of use here.
>
>> > * Call to_char() functions for each placeholder.
>> > For example,
>> > format('=={YYYY-MM-DD}==', tm::timestamp)
>> > is equivalent to
>> > '==' || to_char(tm, 'YYYY-MM-DD') || '=='
>> > '{}' prints the input with the default format.
>> >
>> > New languages' libraries might be of some help. LLs, C#, etc.
>>
>> I though about integration with to_char function too. There are not
>> technical barrier. And I can live with just {to_char_format} too. It
>> can be or cannot be mixed with basic tags together - there is
>> specified a NULL value behave. If we allow {format} syntax, then we
>> have to specify a escape syntax for { and }. Do you have a some idea?
>
> What about %{sth}? That way you don't need to escape {. The closing } would
> need escaping only inside the %{} specifier, so {%{YYYY{\}MM}} prints
> {2010{}08} So the above example is:
then you need escaping too :)
>
> format('==%{YYYY-MM-DD}==', tm::timestamp);
I am not sure if this is correct -but why not
so there are possible combinations
%s .. no quoting, NULL is ''
%{} .. no quoting, NULL is NULL .. like output from to_char
%{}s .. no quoting with formatting, NULL is ''
now I have not idea about nice syntax for positional parameters - maybe
%{...}$1s or we can use a two variants for tags - not positional '%'
and positional '%', so
$1{...}s, %{...}s, $1, %s, $1s, $1{...}, %{...} can be valid tags
Regards
Pavel Stehule
>
> Not sure about this to_char stuff though, seems too cute. You can do
> the case above like this:
>
> format('==%s==', to_char(tm::timestamp, 'YYYY-MM-DD'))
>
I like an using a format like tag - there are not technical problem -
format can be taken from string and data type parameter can be known
too. But this feature can be some enhancing. The basic features are
NULL handling and right quoting.
> --
> Álvaro Herrera <alvherre(at)commandprompt(dot)com>
> The PostgreSQL Company - Command Prompt, Inc.
> PostgreSQL Replication, Consulting, Custom Development, 24x7 support
>
From | Date | Subject | |
---|---|---|---|
Next Message | Pavel Stehule | 2010-08-30 16:21:00 | thousand unrelated data files in pg_default tablespace |
Previous Message | Markus Wanner | 2010-08-30 15:30:59 | Re: bg worker: patch 1 of 6 - permanent process |