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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"Bernhard Reutner-Fischer" <rep.dot.nop@gmail.com> writes:
Fair enough but what about the failure for the case with the Result
that fails to merge? There I do have a cast
No you don't:
select * from (select 'string two' bug ) s2
regards, tom lane
On 10 November 2012 16:58, Tom Lane <tgl@sss.pgh.pa.us> wrote:
"Bernhard Reutner-Fischer" <rep.dot.nop@gmail.com> writes:
Fair enough but what about the failure for the case with the Result
that fails to merge? There I do have a castNo you don't:
select * from (select 'string two' bug ) s2
regards, tom lane
I do not need the cast in the second select when using generate_series
either.
select distinct on (bug) bug
from (
select * from (select 'string one'::text bug from generate_series(0,1))
s1
UNION
select * from (select 'string two' bug) s2
-- select * from (select 'string two' bug from generate_series(0,0)) s2
) x
;
IMO this contradicts the "Type Resolution for UNION, CASE, and Related
Constructs" from the documentation.
4) Choose the first non-unknown input type which is a preferred type in
that category, if there is one.
Please explain why the two selects for 'string two' in the example above
behave different?
Many TIA && cheers,