Thread: What's the meaning of system column in views

Hi all,

I see the following for a view a_view;

# select ctid, xmin, cmin, xmax, cmax, tableoid from a_view;ctid | xmin | cmin | xmax | cmax | tableoid
------+------+------+------+------+----------     |      |      |      |      |     |      |      |      |      |     |
    |      |      |      |     |      |      |      |      |     |      |      |      |      |     |      |      |
|     |     |      |      |      |      |     |      |      |      |      |
 
(8 rows)

All system columns are null and seem to have no 
meaning to me.
In addition it's also annoying to me e.g.

# create view aview as select ctid, * from a_table;
ERROR:  name of column "ctid" conflicts with an existing system column

If there's no objection I would remove system columns 
from views and allow the second example.

regards, 
Hiroshi Inouehttp://w2422.nsk.ne.jp/~inoue/

Hiroshi Inoue <Inoue@tpf.co.jp> writes:
> # create view aview as select ctid, * from a_table;
> ERROR:  name of column "ctid" conflicts with an existing system column

> If there's no objection I would remove system columns 
> from views and allow the second example.

I seem to recall having looked at this awhile back and deciding that it
was harder than it was worth.  But if you can do it I have no objection.
(It might be easier now than it was then; I think there are fewer places
now that have hardwired knowledge about system columns than before.)
        regards, tom lane