Re: string function - "format" function proposal - Mailing list pgsql-hackers

2010/8/30 Alvaro Herrera <alvherre@commandprompt.com>:
> Excerpts from Pavel Stehule's message of lun ago 30 07:51:55 -0400 2010:
>> 2010/8/30 Itagaki Takahiro <itagaki.takahiro@gmail.com>:
>> > On Mon, Aug 30, 2010 at 7:58 PM, Pavel Stehule <pavel.stehule@gmail.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.



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> Álvaro Herrera <alvherre@commandprompt.com>
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