On Sat, Aug 1, 2009 at 6:49 PM, Andy Colson <andy@xxxxxxxxxxxxxxx
<mailto:andy@xxxxxxxxxxxxxxx>> wrote:
Andy Colson wrote:
Jun Yang wrote:
Hi all,
I want to add some common columns to all of my tables. One
way I
think would be to add a super table that contains the common
columns
to all tables. But is there a way to add a super table to
existing
tables for them to inherit from?
Thanks!
Jun
as long as the parent and child has the same table struct, yes.
use:
alter table child inherit newparent;
-Andy
err... sorry, let me fix that: the parent must have a common subset
of all the children. (The children can have extras the parent does
not, but not visa versa)
Jun Yang wrote:
Thanks a lot for your reply, Andy!
That means no then because my child tables are not like the parent at
all. If the parent has a subset of child's columns, what does that mean
because I thought the whole point of inheritance is so that child tables
don't need to define common columns repeatedly using inheriting them
from the parent.
Jun
Please keep the group on the list.
In the docs, you can see that yes, you are correct, if setup from the beginning, the children dont need the parent fields.
http://www.postgresql.org/docs/8.4/interactive/ddl-inherit.html
-- the parent
CREATE TABLE cities (
name text,
population float,
altitude int -- in feet
);
-- the child
CREATE TABLE capitals (
state char(2)
) INHERITS (cities);
But you're doing it after the fact. I tried it out, it doenst work:
andy=# create table capitals (state varchar(2));
CREATE TABLE
Time: 17.754 ms
andy=# create table cities(name text);
CREATE TABLE
Time: 1.971 ms
andy=# alter table capitals INHERIT cities;
ERROR: child table is missing column "name"
andy=#
-Andy
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