Re: Reinterpreting BYTEA as TEXT, converting BYTEA to TEXT

On Wed, Mar 9, 2011 at 4:09 PM, Vlad Romascanu <vromascanu(at)accurev(dot)com> wrote:
> Hello,
>
> I need to perform "conversions" (transcoding) between BYTEA and TEXT
> columns in a UTF-8 database.  I searched for existing solutions and
> was unable to find one for 8.x or 9.x, so I cam up with something I'd
> like to validate with the more enlightened members of this list...
>
> Case 1: reinterpreting:
>
> (Working on a 8.4.3 backend.)
>
> In a UTF8 database I have a BYTEA value which contains a perfectly
> valid UTF8 string.  I want to simply *reinterpret* it as TEXT (in the
> same way pg_convert_from internally reinterprets the BYTEA return
> value from pg_convert as TEXT), backend-side, no
> transcoding/encoding/decoding should take place.
>
> The solution I came up with goes something like this:
>
>  CREATE DOMAIN my_varlena AS bytea;
>  CREATE CAST (my_varlena AS text) WITHOUT FUNCTION;
>  ...
>  SELECT bytea_col::my_varlena::text FROM tbl; -- bypass the bytea to
> varchar/text conversion which actually calls encode()
>  ...
>  DROP DOMAIN my_varlena CASCADE;
>
> Is there anything blatantly wrong with this approach that I have
> missed, or is there a more straightforward way, or anything to be
> improved?  (Again, I need a backend-side solution, not a client-side
> one -- e.g. copying huge amounts of data from a BYTEA column to a TEXT
> column in some other table.)

I think convert_from is a little more direct:
convert_from(string bytea, src_encoding name)
http://www.postgresql.org/docs/8.4/interactive/functions-string.html

merlin