Re: String literal doesn't autocast to text type

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

"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
<http://www.postgresql.org/docs/9.4/interactive/datatype-oid.html>); this
means that it is the same as an OID for comparison purposes but displays as
a type name. For example:"

Please in the future, ALWAYS specify your PostgreSQL version and O/S,
regardless of whether or not you thinnk it is pertinent.

On Fri, Mar 4, 2016 at 12:17 PM, Alex Ignatov <a(dot)ignatov(at)postgrespro(dot)ru>
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
wish to share my fantasy is entirely up to you.