Re: Rules and actions involving multiple rows

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Re: Rules and actions involving multiple rows

От:
Alvaro Herrera <alvherre@dcc.uchile.cl>
Дата:
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 ()
"Limitate a mirar... y algun dia veras"

Rules and actions involving multiple rows

От:
Jason Godden <jasongodden@optushome.com.au>
Дата:
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

От:
Bruce Momjian <pgman@candle.pha.pa.us>
Дата:

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
> 

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Re: Rules and actions involving multiple rows

От:
Dmitry Tkach <dmitry@openratings.com>
Дата:
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
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