Re: patch: to_string, to_array functions

On Wed, Jul 21, 2010 at 12:39 AM, Itagaki Takahiro
<itagaki(dot)takahiro(at)gmail(dot)com> wrote:
> 2010/7/20 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
>> here is a new version - new these functions are not a strict and
>> function to_string is marked as stable.
>
> We have array_to_string(anyarray, text) and string_to_array(text, text),
> and you'll introduce to_string(anyarray, text, text) and
> to_array(text, text, text).
> Do we think it is good idea to have different names for them?  IMHO, we'd
> better  use 3 arguments version of array_to_string() instead of the
> new to_string() ?

The worst part is that the new names are not very mnemonic.

I think maybe what we really need here is array equivalents of
COALESCE() and NULLIF(). It looks like the proposed to_string()
function is basically equivalent to replacing each NULL entry with the
array with a given value, and then doing array_to_string() as usual.
And it looks like the proposed to_array function basically does the
same thing as to_array(), and then replaces empty strings with NULL or
some other value.

Maybe we just need a function array_replace(anyarray, anyelement,
anyelement) that replaces any element in the array that IS NOT
DISTINCT FROM $2 with $3 and returns the new array. That could be
useful for other things besides this particular case, too.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company