Обсуждение: unimplemented functions

I'm new to postgres and pgadmin3 (on Windows XP).

I've just tried to make a change to a table using pgAdmin3 (1.0.2) and I
get:-

---------------------------
pgAdmin III
---------------------------
An error has occured:

ERROR:  adding columns with defaults is not implemented
HINT:  Add the column, then use ALTER TABLE SET DEFAULT.

---------------------------
OK
---------------------------

When will this be fixed? Is this the right forum for discussing
unimplemented fuctions? Is there somewhere or someone specific to point is
out with?

chris@zenmgt.com wrote:

> I'm new to postgres and pgadmin3 (on Windows XP).
>
> I've just tried to make a change to a table using pgAdmin3 (1.0.2) and
> I get:-
>
> ---------------------------
> pgAdmin III
> ---------------------------
> An error has occured:
>
> ERROR:  adding columns with defaults is not implemented
> HINT:  Add the column, then use ALTER TABLE SET DEFAULT.
>
> ---------------------------
> OK
> ---------------------------
>
> When will this be fixed? Is this the right forum for discussing
> unimplemented fuctions? Is there somewhere or someone specific to
> point is out with?


Chris,

This isn't a pgadmin bug--it is a limitation of Postgres. You can't add
a column to a table *and* set a default value for it all in one
statement. Try the hint that is given: add the column, then alter the
column to set the default value. You can read the details of using the
ALTER command in the Postgres online documentation.

Regards,

Bill Montgomery

chris@zenmgt.com writes:
> ERROR:  adding columns with defaults is not implemented
> HINT:  Add the column, then use ALTER TABLE SET DEFAULT.

> When will this be fixed?

Probably not very soon, as it is easily worked around, and the
spec-mandated behavior is not necessarily what you want anyway.

ALTER TABLE t ADD COLUMN c INT DEFAULT 42;

is equivalent per SQL spec to

ALTER TABLE t ADD COLUMN c INT;
ALTER TABLE t ALTER COLUMN c SET DEFAULT 42;
UPDATE t SET c = DEFAULT;

That last step is fairly expensive since it forces an update of every
row of the table.  (The ALTERs themselves only touch catalog data and
are cheap even with large tables.)  If you are intending to load the new
column with non-default values then you probably don't really want the
UPDATE step.  Without it, the new column will read as NULL until you
get around to setting it.

            regards, tom lane