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Re: string function - "format" function proposal

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: string function - "format" function proposal
Date: 2010-08-30 11:51:55
Message-ID: AANLkTimfkWVrpNz_r2FL0aS7hhhC_hX27tEq4vuJyJh2@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
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.

> * 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?

Regards

Pavel



>
> --
> Itagaki Takahiro
>

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