Обсуждение: BUG #7644: Missing implicit types of Result and failing type-conversion

The following bug has been logged on the website:

Bug reference:      7644
Logged by:          Bernhard Reutner-Fischer
Email address:      rep.dot.nop@gmail.com
PostgreSQL version: 9.1.6
Operating system:   debian
Description:        =


Hi,

According to
http://www.postgresql.org/docs/9.1/static/typeconv-union-case.html

i think that these 2 (separate?) issues are bugs(?)
1)
select distinct on (bug) bug
from (
        select * from (select 'string one' AS bug from generate_series(0,1))
s1
        UNION
        select * from (select 'string two' bug from generate_series(0,0))
s2
     ) x
;
ERROR:  could not determine which collation to use for string comparison
HINT:  Use the COLLATE clause to set the collation explicitly.

When casting the return value of the union to :text _explicitly_ it works as
expected:
select distinct on (bug) bug
from (
        select * from (select 'string one'::text AS bug from
generate_series(0,1)) s1
        UNION
        select * from (select 'string two' bug from generate_series(0,0))
s2
     ) x
;
    bug     =

------------
 string one
 string two
(2 rows)

2)
select distinct on (bug) bug
from (
        select * from (select 'string one' AS bug from generate_series(0,1))
s1
        UNION
        select * from (select 'string two' bug) s2
     ) x
;
ERROR:  failed to find conversion function from unknown to text

In this case, however, using a "Result" fails to implicitly typecast to
:text, i.e. casting the return value of the first return value of the union
to :text explicitly does _not_ work:

select distinct on (bug) bug
from (
        select * from (select 'string one'::text AS bug from
generate_series(0,1)) s1
        UNION
        select * from (select 'string two' bug ) s2                        =


     ) x
;
ERROR:  failed to find conversion function from unknown to text

What am i missing or doing wrong?
thanks and cheers,

rep.dot.nop@gmail.com writes:
> select distinct on (bug) bug
> from (
>         select * from (select 'string one' AS bug from generate_series(0,1))
> s1
>         UNION
>         select * from (select 'string two' bug from generate_series(0,0))
> s2
>      ) x
> ;
> ERROR:  could not determine which collation to use for string comparison
> HINT:  Use the COLLATE clause to set the collation explicitly.

> What am i missing or doing wrong?

Leaving out the cast.  An undecorated string literal is not a constant
of type text --- it is a constant of unknown type, and the parser will
throw an error if the type can't be resolved from fairly-local context.
(The same applies to NULL, btw.)

            regards, tom lane

On 10 November 2012 16:20:24 Tom Lane <tgl@sss.pgh.pa.us> wrote:
> rep.dot.nop@gmail.com writes:
> > select distinct on (bug) bug
> > from (
> >         select * from (select 'string one' AS bug from generate_series(0,1))
> > s1
> >         UNION
> >         select * from (select 'string two' bug from generate_series(0,0))
> > s2
> >      ) x
> > ;
> > ERROR:  could not determine which collation to use for string comparison
> > HINT:  Use the COLLATE clause to set the collation explicitly.
>
> > What am i missing or doing wrong?
>
> Leaving out the cast.  An undecorated string literal is not a constant
> of type text --- it is a constant of unknown type, and the parser will
> throw an error if the type can't be resolved from fairly-local context.
> (The same applies to NULL, btw.)

Fair enough but what about the failure for the case with the Result
that fails to merge? There I do have a cast but it fails on the Result
as opposed to a genera e_series(0,0):

select distinct on (bug) bug
from (
        select * from (select 'string one'::text AS bug from
generate_series(0,1)) s1
        UNION
        select * from (select 'string two' bug ) s2

     ) x
;


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