Re: why generated columsn cannot be used in COPY TO?

On 10/6/23 07:20, Andreas Kretschmer wrote:
>
>
> Am 06.10.23 um 13:53 schrieb Luca Ferrari:
>> Hi all,
>> I'm wondering why in COPY TO (file or program) I cannot use generated
>> columns: since I'm pushing data out of the table, why they are not
>> allowed?
>>
>> Example:
>>
>> testdb=# CREATE TABLE test( pk int generated always as identity primary key
>> , ts timestamp default current_timestamp
>> , month int generated always as ( extract( month from ts ) ) stored
>> );
>>
>> testdb=# insert into test( ts ) values( current_timestamp );
>>
>> testdb=# copy test to program 'head'; -- ok but silently removes the column
>> COPY 1
>> testdb=# copy test( month ) to program 'head';
>> ERROR:  column "month" is a generated column
>> DETAIL:  Generated columns cannot be used in COPY.
>
> you can use copy (select * ...) to ...

But why not?

--
Born in Arizona, moved to Babylonia.