Hi,
On 2013-11-13 08:52:27 +0100, Luca Ferrari wrote:
> when you drop a column on a table the pg_attribute is updated and the
> name of the column is changed with an almost fixed identifier that
> reports only the original column position:
>
> /*
> * Change the column name to something that isn't likely to conflict
> */
> snprintf(newattname, sizeof(newattname),
> "........pg.dropped.%d........", attnum);
> namestrcpy(&(attStruct->attname), newattname);
>
> I'm wondering what is the problem in placing the old/original name
> after the "pg.dropped" prefix. I know that the tuple in pg_attribute
> is temporary, but what are the possible conflicts the comment talks
> about?
The old name might not fit there, attribute names have a relatively low
maximum length (64 by default), so we cannot always fit the entire old
name there.
Also, think about:
CREATE TABLE foo(cola int);
ALTER TABLE foo DROP COLUMN cola;
ALTER TABLE foo ADD COLUMN cola;
ALTER TABLE foo DROP COLUMN cola; -- should not error out
I don't really see much need for anything better than the current
solution, why is the old name interesting?
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
