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* Update instead rules on Views
@ 2004-11-02 12:05 Markus Schaber <schabios@logi-track.com>
0 siblings, 1 reply; 3+ messages in thread
From: Markus Schaber @ 2004-11-02 12:05 UTC (permalink / raw)
To: pgsql-sql
Hello,
It seems that I have a fundamental misunderstanding how views work.
See the following example:
--- snip snap ---
CREATE TABLE realdata (index int, data varchar, obsolete int);
COPY realdata FROM STDIN;
1 hallo \N
2 test \N
3 blubb \N
\.
-- The obsolete row is a row that is now to be calculated on the
-- fly. In our real data, this is to be a nested select, but random()
-- works for this example as well.
CREATE VIEW testview AS
SELECT index, data, (random()*99)::int from realdata;
-- But to remain compatibility with old apps, we also need to manage
-- updates to the view, which are to be rewritten as follows:
CREATE RULE testview_update_rule
AS ON UPDATE TO testview DO INSTEAD
UPDATE realdata SET
index = NEW.index,
data = NEW.data,
obsolete=NULL
;
--- snip snap ---
But now, when we issue an
UPDATE testview SET data='nono' WHERE index=1;
we get the result
UPDATE 3
So it updated _all_ of the rows instead of the qualified rows (WHERE index=1).
SELECT * FROM realdata;
index | data | obsolete
-------+------+----------
1 | nono |
1 | nono |
1 | nono |
But the documentation states: (rules-update.html):
| No qualification but INSTEAD
|
| the query tree from the rule action with the original query
| tree's qualification added
I read this that the original qualification (WHERE index=1) is applied
to the rule, resulting in a transformed query equivalent to:
UPDATE realdata SET data='nono' WHERE index=1;
which works as expected.
Can anyone enlighten me?
Thanks,
Markus
PS: My server version is PostgreSQL 7.4.5 on i386-pc-linux-gnu, compiled by GCC i386-linux-gcc (GCC) 3.3.4 (Debian 1:3.3.4-9)
--
markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
phone +41-43-888 62 52 | fax +41-43-888 62 53
mailto:schabios@logi-track.com | www.logi-track.com
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Update instead rules on Views
@ 2004-11-02 15:20 Markus Schaber <schabios@logi-track.com>
parent: Markus Schaber <schabios@logi-track.com>
0 siblings, 1 reply; 3+ messages in thread
From: Markus Schaber @ 2004-11-02 15:20 UTC (permalink / raw)
To: pgsql-sql
Helo,
On Tue, 2 Nov 2004 13:05:07 +0100
Markus Schaber <schabios@logi-track.com> wrote:
> -- But to remain compatibility with old apps, we also need to manage
> -- updates to the view, which are to be rewritten as follows:
> CREATE RULE testview_update_rule
> AS ON UPDATE TO testview DO INSTEAD
> UPDATE realdata SET
> index = NEW.index,
> data = NEW.data,
> obsolete=NULL
> ;
I now got it to work with adding a "WHERE index=NEW.index" to the view.
Am I correct in my assumption that this means that this only works when
I have a primary key (or at least unique) row in my dataset?
Thanks,
Markus
--
markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
phone +41-43-888 62 52 | fax +41-43-888 62 53
mailto:schabios@logi-track.com | www.logi-track.com
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Update instead rules on Views
@ 2004-11-02 15:42 Markus Schaber <schabios@logi-track.com>
parent: Markus Schaber <schabios@logi-track.com>
0 siblings, 0 replies; 3+ messages in thread
From: Markus Schaber @ 2004-11-02 15:42 UTC (permalink / raw)
To: pgsql-sql
Hello,
On Tue, 2 Nov 2004 16:20:37 +0100
Markus Schaber <schabios@logi-track.com> wrote:
> > -- But to remain compatibility with old apps, we also need to manage
> > -- updates to the view, which are to be rewritten as follows:
> > CREATE RULE testview_update_rule
> > AS ON UPDATE TO testview DO INSTEAD
> > UPDATE realdata SET
> > index = NEW.index,
> > data = NEW.data,
> > obsolete=NULL
> > ;
>
> I now got it to work with adding a "WHERE index=NEW.index" to the view.
This seems only to work when I update on the INDEX row. I now modified
the rule to look like:
CREATE RULE testview_update_rule
AS ON UPDATE TO testview DO INSTEAD
UPDATE realdata SET
index = NEW.index,
data = NEW.data,
obsolete=NULL
WHERE index = OLD.index;
This seems to work now for arbitrary columns, provided that index is an
unique row.
When I have a table that looks like
index | data | obsolete
-------+-------+----------
2 | test |
3 | blubb |
1 | nono |
3 | hallo |
and I issue
viewtest=# update testview set data='blob' where data='hallo';
I get:
UPDATE 2
and it really updated 2 rows.
As far as I understand now, I need a primary key in the underyling table
as the qualification from the original statemet is applied to the view
results, and not propagated to the underlying table.
Thanks,
Markus
--
markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
phone +41-43-888 62 52 | fax +41-43-888 62 53
mailto:schabios@logi-track.com | www.logi-track.com
^ permalink raw reply [nested|flat] 3+ messages in thread
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2004-11-02 12:05 Update instead rules on Views Markus Schaber <schabios@logi-track.com>
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2004-11-02 15:42 ` Markus Schaber <schabios@logi-track.com>
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