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Thread: Rules and actions involving multiple rows

Rules and actions involving multiple rows

From
Jason Godden
Date:
Hi All,

Just have a quick question regarding rules:

In the past I've always used triggers to fire before or after events however I
see that the same thing can be achieved through rules (for logging etc...) so
I created a rule which fires on update (not DO INSTEAD) however it only seems
to work for a single row - whereas the triggers work for all rows updated in
a transaction.  Is this correct and if so I presume I should be sticking to
triggers if I want this kind of behaviour?

Rgds,

Jason

Re: Rules and actions involving multiple rows

From
Alvaro Herrera
Date:
On Sun, Jul 06, 2003 at 02:48:59PM +1000, Jason Godden wrote:

> In the past I've always used triggers to fire before or after events however I
> see that the same thing can be achieved through rules (for logging etc...) so
> I created a rule which fires on update (not DO INSTEAD) however it only seems
> to work for a single row - whereas the triggers work for all rows updated in
> a transaction.

Rules are a once-per-statement thing, and thus appear to be "for a
single row."  Triggers can be once-per-row or once-per-statement.  Only
you know what is more appropiate in your scenario...

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"Limitate a mirar... y algun dia veras"

Re: Rules and actions involving multiple rows

From
Dmitry Tkach
Date:
Jason Godden wrote:

>Hi All,
>
>Just have a quick question regarding rules:
>
>In the past I've always used triggers to fire before or after events however I
>see that the same thing can be achieved through rules (for logging etc...) so
>I created a rule which fires on update (not DO INSTEAD) however it only seems
>to work for a single row - whereas the triggers work for all rows updated in
>a transaction.  Is this correct and if so I presume I should be sticking to
>triggers if I want this kind of behaviour?
>
>Rgds,
>
>
Hmmm... Works for me... :

testdb=# create table x (x int);
CREATE TABLE
testdb=# create table old_x (x int);
CREATE TABLE
testdb=# insert into x values (1);
INSERT 17204 1
testdb=# insert into x values (2);
INSERT 17205 1
testdb=# create rule xup as on update to x do insert into old_x values
(old.*);
CREATE RULE
testdb=# update x set x=0;
UPDATE 2
testdb=# select * from old_x;
 x
---
 1
 2
(2 rows)



Or were you talking about something else?

Dima

Re: Rules and actions involving multiple rows

From
Bruce Momjian
Date:
For me, triggers are for modifying the row being
updated/deleted/inserted, while rules are for modifying other rows as
part of the query.

---------------------------------------------------------------------------

Jason Godden wrote:
> Hi All,
>
> Just have a quick question regarding rules:
>
> In the past I've always used triggers to fire before or after events however I
> see that the same thing can be achieved through rules (for logging etc...) so
> I created a rule which fires on update (not DO INSTEAD) however it only seems
> to work for a single row - whereas the triggers work for all rows updated in
> a transaction.  Is this correct and if so I presume I should be sticking to
> triggers if I want this kind of behaviour?
>
> Rgds,
>
> Jason
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
>       joining column's datatypes do not match
>

--
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