Обсуждение: altering a column to to make it generated

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altering a column to to make it generated

От
Celia McInnis
Дата:
Can I alter a table column to now make it generated? I tried this unsuccessfully:

create temp table tmp1 as select 15::numeric(6,1) as distance,'24:30'::interval,0::numeric(7,3) as avgspd;
alter table tmp1 alter column avgspd type numeric(7,3) generated always as ((3600.*distance)/EXTRACT (EPOCH FROM rdrtime::interval)) STORED;
ERROR:  syntax error at or near "generated"
LINE 1: ... table tmp1 alter column avgspd type numeric(7,3) generated ...

I think that at least I have the right bracketing this time! :-)                                                             ^




Re: altering a column to to make it generated

От
"David G. Johnston"
Дата:
On Mon, Apr 22, 2024 at 12:42 PM Celia McInnis <celia.mcinnis@gmail.com> wrote:
Can I alter a table column to now make it generated? I tried this unsuccessfully:

I looked at all of the "alter table ... alter column" commands listed here:

https://www.postgresql.org/docs/current/sql-altertable.html

And none seem to involve the generated expression column.  So the answer is no.

David J.

Re: altering a column to to make it generated

От
Adrian Klaver
Дата:
On 4/22/24 12:42, Celia McInnis wrote:
> Can I alter a table column to now make it generated? I tried this 
> unsuccessfully:
> 
> create temp table tmp1 as select 15::numeric(6,1) as 
> distance,'24:30'::interval,0::numeric(7,3) as avgspd;
> alter table tmp1 alter column avgspd type numeric(7,3) generated always 
> as ((3600.*distance)/EXTRACT (EPOCH FROM rdrtime::interval)) STORED;
> ERROR:  syntax error at or near "generated"
> LINE 1: ... table tmp1 alter column avgspd type numeric(7,3) generated ...
> 
> I think that at least I have the right bracketing this time! :-) 

See David Johnston's comment. I keep on wanting to believe that ALTER 
TABLE supports GENERATED expressions, when it only supports GENERATED 
IDENTITY:)

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> 
> 
> 
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com

Re: altering a column to to make it generated

От
Tom Lane
Дата:
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Mon, Apr 22, 2024 at 12:42 PM Celia McInnis <celia.mcinnis@gmail.com>
> wrote:
>> Can I alter a table column to now make it generated? I tried this
>> unsuccessfully:

> I looked at all of the "alter table ... alter column" commands listed here:
> https://www.postgresql.org/docs/current/sql-altertable.html
> And none seem to involve the generated expression column.  So the answer is
> no.

I think what you'd need to do is drop the existing column
and then add a generated column.

            regards, tom lane