Обсуждение: Implicit/Explicit casting of the unknown type

Hi,

I am new to this list. I have browsed the list archives and tried a
search, but haven't found anything about my problem.

I am porting several applications to PostgreSQL and have come across a
number of instances where a string literal does not work without an
explicit cast to some character based datatype. Two examples are given
below: one where the string literal is in the column list, and one where
it is in a WHERE clause.

Are there bugs in the area of determining a type for the unknown type?
Or is explicit casting of string literals to a known type generally
required by PostgreSQL?

TIA,

Stephen Jackson
Home: Stephen.Jackson@panting-deer.org.uk  www.panting-deer.org.uk
Work: Stephen.Jackson@looksystems.co.uk    www.looksystems.co.uk

[begin examples]                              version                               
---------------------------------------------------------------------PostgreSQL 7.0.3 on i686-pc-linux-gnu, compiled by
gccegcs-2.91.66
 
(1 row)

DROP TABLE strange
DROP
CREATE TABLE strange ( record_id integer )
CREATE
INSERT INTO strange ( record_id ) VALUES ( 10 )
INSERT 5174249 1
SELECT DISTINCT record_id, 123
FROM strange WHERE record_id < 100record_id | ?column? 
-----------+----------       10 |      123
(1 row)

SELECT DISTINCT record_id, 'Hello'
FROM strange WHERE record_id < 100
ERROR:  Unable to identify an ordering operator '<' for type 'unknown'Use an explicit ordering operator or modify the
query
SELECT record_id, 'Hello'
FROM strange WHERE record_id < 100record_id | ?column? 
-----------+----------       10 | Hello
(1 row)

SELECT COUNT(*) FROM strange
WHERE 'TR' || 'UE' = 'TRUE'count 
-------    1
(1 row)

SELECT COUNT(*) FROM strange
WHERE 'TRUE' = 'TRUE'
ERROR:  Unable to identify an operator '=' for types 'unknown' and
'unknown'You will have to retype this query using an explicit cast

[end examples]

Hi,

Apologies for re-posting - this problem is giving me a bit of a
headache.
Basically, my problem is that in a number of (to me surprising) contexts
an explicit cast from a string literal to some character data type is
required by PostgreSQL, where such casts are not required by other rdbms
with which I am more familiar. (Examples below.) Is there a rule of
thumb I can use to tell when such a cast is required?

I hope someone can help.

Regards,

Stephen Jackson
Home: Stephen.Jackson@panting-deer.org.uk  www.panting-deer.org.uk
Work: Stephen.Jackson@looksystems.co.uk    www.looksystems.co.uk

On Mon, 26 Mar 2001 21:03:55 +0100, Stephen Jackson wrote:
> 
> Hi,
> 
> I am new to this list. I have browsed the list archives and tried a
> search, but haven't found anything about my problem.
> 
> I am porting several applications to PostgreSQL and have come across a
> number of instances where a string literal does not work without an
> explicit cast to some character based datatype. Two examples are given
> below: one where the string literal is in the column list, and one where
> it is in a WHERE clause.
> 
> Are there bugs in the area of determining a type for the unknown type?
> Or is explicit casting of string literals to a known type generally
> required by PostgreSQL?
> 
> TIA,
> 
> Stephen Jackson
> Home: Stephen.Jackson@panting-deer.org.uk  www.panting-deer.org.uk
> Work: Stephen.Jackson@looksystems.co.uk    www.looksystems.co.uk
> 
> [begin examples]
>                                version
> ---------------------------------------------------------------------
>  PostgreSQL 7.0.3 on i686-pc-linux-gnu, compiled by gcc egcs-2.91.66
> (1 row)
> 
> DROP TABLE strange
> DROP
> CREATE TABLE strange ( record_id integer )
> CREATE
> INSERT INTO strange ( record_id ) VALUES ( 10 )
> INSERT 5174249 1
> SELECT DISTINCT record_id, 123
> FROM strange WHERE record_id < 100
>  record_id | ?column?
> -----------+----------
>         10 |      123
> (1 row)
> 
> SELECT DISTINCT record_id, 'Hello'
> FROM strange WHERE record_id < 100
> ERROR:  Unable to identify an ordering operator '<' for type 'unknown'
>         Use an explicit ordering operator or modify the query
> SELECT record_id, 'Hello'
> FROM strange WHERE record_id < 100
>  record_id | ?column?
> -----------+----------
>         10 | Hello
> (1 row)
> 
> SELECT COUNT(*) FROM strange
> WHERE 'TR' || 'UE' = 'TRUE'
>  count
> -------
>      1
> (1 row)
> 
> SELECT COUNT(*) FROM strange
> WHERE 'TRUE' = 'TRUE'
> ERROR:  Unable to identify an operator '=' for types 'unknown' and
> 'unknown'
>         You will have to retype this query using an explicit cast
> 
> [end examples]
>

Steve,
Hmmm ... I'm using PostgreSQL for quite a few contortions of data, and
I can't say that I've encountered anything quite like the problems
you're having.  It may be that you actually have a compile problem with
Postgres rather than a SQL problem.
                -Josh

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