Probably because pg_typeof() returns the OID of a COLUMN in a table def.. Strings literals do not have oid's.
http://www.postgresql.org/docs/9.4/interactive/functions-info.html
Please in the future, ALWAYS specify your PostgreSQL version and O/S, regardless of whether or not you thinnk it is pertinent.http://www.postgresql.org/docs/9.4/interactive/functions-info.html
"pg_typeof returns the OID of the
data type of the value that is passed to it. This can be helpful
for troubleshooting or dynamically constructing SQL queries. The
function is declared as returning regtype,
which is an OID alias type (see Section 8.18); this means that it is the
same as an OID for comparison purposes but displays as a type
name. For example:"On Fri, Mar 4, 2016 at 12:17 PM, Alex Ignatov <a.ignatov@xxxxxxxxxxxxxx> wrote:
Hello!
Why string literal like 'Hello world!' doesnt automagicaly cast to text type?
postgres=# select pg_typeof('Hello world');
pg_typeof
-----------
unknown
(1 row)
But for example literal like 1.1 automagically cast to numeric( not float8, float4, whatever)
postgres=# select pg_typeof(1.1);
pg_typeof
-----------
numeric
(1 row)
That why we cant do the following without explicit type casting:
postgres=# select t.c||' world' from (select 'Hello' as c) as t;
ERROR: failed to find conversion function from unknown to text
but that ok:
postgres=# select t.c||' world' from (select 'Hello'::text as c) as t;
?column?
-------------
Hello world
(1 row)
or this is ok too:
postgres=# select t.c::text||' world' from (select 'Hello' as c) as t;
?column?
-------------
Hello world
(1 row)
Sure we can create our cast:
postgres=# create cast (unknown as text) with inout as implicit;
CREATE CAST
and after that we have:
postgres=# select t.c||' world' from (select 'Hello' as c) as t;
?column?
-------------
Hello world
(1 row)
But why we don't have this type cast by default in Postgres? Is there any fundamental restriction on that or there is some reasons for that?
--
Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
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Melvin Davidson
I reserve the right to fantasize. Whether or not you
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I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
