Re: modifying views

On Wed, 2 Feb 2005 11:16:56 +0200, Sim Zacks <sim(at)nospam(dot)com> wrote:
> I read the following thread from Nov 2002 on the impossibilities of
> modifying a view and I was wondering if anything had changed in this regard
> since then?
> http://archives.postgresql.org/pgsql-hackers/2002-11/msg00609.php
>
> Basically I want to remove a column from a table. The column is used in a
> view. The view, but not the column that I want to remove, is used in 24
> other views. A number of those views are also used in other views...
>
> I can't remove the columns from the view without dropping over 100 other
> views, removing the columns from this view and recreating them. I was able
> to remove the columns from the table by modifying the view so instead of
> "table1.field1" it has "null::varchar as field1"
> The problem is that the field is still in the view and I don't want it there
> (obviously).
>
> I read somewhere that a possible solution would be to do a pg_dump, manually
> change the text file and then do a pg_restore. Unfortunately, that means
> taking the system offline, which I can't do.

Actually, you shouldn't have to take the system down at all.

1) Do a 'pg_dump -s', which will give you just the schema of the DB.

2) Trim this file down to the create statements for the table and all
the dependant views, add the "DROP VIEW baseview CASCADE" and "ALTER
TABLE ... DROP COLUMN ..." statements to the top, and change the base
view's definition.

2a) (this is the REALLY important part!) put "BEGIN;" at the top and
DO NOT(!!!) put "COMMIT;" at the bottom, but DO put some test SELECTs
that will touch the base view and the dependant views to make sure
they are intact, and that the column is gone.

3) Use \i from within the psql console to run that SQL script. The
script will be run inside a transaction, and the changes wont be
visible to anyone else until you type COMMIT;.

If the output of the test SELECTs looks good just commit the change.
If you are unsure, or something seems to have gone wrong just type
"ROLLBACK;" and everything will be back the way is was before!

The only downtime will be the few seconds it takes to alter the table,
recreate the views, and inspect that everything is still OK. If you
want to test safely you could do a full load of 'pg_dump -s' (again,
just the schema) into a temp database and test the script there.

> I could use any help that you can give me.
> Thanks
> Sim

Hope that counts as help!

--
Mike Rylander
mrylander(at)gmail(dot)com
GPLS -- PINES Development
Database Developer
http://open-ils.org