Re: SELECT my_table.varchar FROM my_table

Hello,

I accidentally encountered a feature in Postgres 8.3 that I couldn't
find in the documentation while submitting a query like

SELECT my_table.varchar FROM my_table

which returns a concatenated string of all field values per row.
I wonder where this is documented (and if it has something to do with
composite types).

Can anyone please explain?

Thanks,
Jan

On Mon, May 31, 2010 at 7:48 AM, Jan Strube <js(at)deriva(dot)de> wrote:

> I accidentally encountered a feature in Postgres 8.3 that I couldn't find in
> the documentation while submitting a query like
>
> SELECT my_table.varchar FROM my_table
>
> which returns a concatenated string of all field values per row.
> I wonder where this is documented (and if it has something to do with
> composite types).
>
> Can anyone please explain?

I don't really know, but the result looks more like a single field
formatted as "ROW-WISE" rather than CSV. The official way to get this
result is:

SELECT ROW( my_table.* ) FROM my_table;

http://www.postgresql.org/docs/9.0/static/sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS

--
Regards,
Richard Broersma Jr.

Visit the Los Angeles PostgreSQL Users Group (LAPUG)
http://pugs.postgresql.org/lapug

Richard Broersma <richard(dot)broersma(at)gmail(dot)com> writes:
> On Mon, May 31, 2010 at 7:48 AM, Jan Strube <js(at)deriva(dot)de> wrote:
>> I accidentally encountered a feature in Postgres 8.3 that I couldn't find in
>> the documentation while submitting a query like
>>
>> SELECT my_table.varchar FROM my_table
>>
>> which returns a concatenated string of all field values per row.
>> I wonder where this is documented (and if it has something to do with
>> composite types).
>>
>> Can anyone please explain?

> I don't really know, but the result looks more like a single field

It's equivalent to (my_table.*)::varchar. We've seen enough people
confused by this (or the equivalent cases with text and name as
the target type) that I wonder if we should intentionally break the
symmetry and disable treating this case as a cast. Although I do
rather wonder what the OP expected to happen here.

regards, tom lane

Am 31.05.2010 17:44, schrieb Tom Lane:
> Richard Broersma<richard(dot)broersma(at)gmail(dot)com> writes:
>
>> On Mon, May 31, 2010 at 7:48 AM, Jan Strube<js(at)deriva(dot)de> wrote:
>>
>>> I accidentally encountered a feature in Postgres 8.3 that I couldn't find in
>>> the documentation while submitting a query like
>>>
>>> SELECT my_table.varchar FROM my_table
>>>
>>> which returns a concatenated string of all field values per row.
>>> I wonder where this is documented (and if it has something to do with
>>> composite types).
>>>
>>> Can anyone please explain?
>>>
>
>> I don't really know, but the result looks more like a single field
>>
> It's equivalent to (my_table.*)::varchar. We've seen enough people
> confused by this (or the equivalent cases with text and name as
> the target type) that I wonder if we should intentionally break the
> symmetry and disable treating this case as a cast. Although I do
> rather wonder what the OP expected to happen here.
>

I didn't expect anything special, because my original statement was
actually a typo. So I was just amazed that I didn't get an error.

Thanks for the explanation,
Jan