Обсуждение: automatic update

Hi to all ...

I'm looking to a way to auto update some fields of a row when other
fileds are updated.

the table structure are simple,

CREATE TABLE param (
id int4 PRIMARY KEY,
val int4,
ts timestam(3) DEFAULT CURRENT_TIMESTAMP
);

so when a new entry are insert ts areautomatically update,
but i would make the same on update ...

i would that on
UDPATE param SET val=100 WHERE id=1;

also ts field have to be updated to CURRENT_TIMESTAMP

I try with a RULE but obtain only a loop, seem RULE aren't good to make
such things, modify a statment on the same table it's related :(

i look for a trigger but I suppose the same problem arise ...

how i can solve the problem ???

mhhh does i have to have a VIEW of parm ... called param2 without the ts
field and make a rule on param2 that update param.ts ???
seem a bit tricky :( ...

thanks in advance ...


--
Alessandro GARDICH <gremlin@gremlin.it>
gremlin.it

On Tuesday 02 September 2003 09:34, Alessandro GARDICH wrote:
> Hi to all ...
>
> I'm looking to a way to auto update some fields of a row when other
> fileds are updated.
>
> the table structure are simple,
>
> CREATE TABLE param (
> id int4 PRIMARY KEY,
> val int4,
> ts timestam(3) DEFAULT CURRENT_TIMESTAMP
> );
>
> so when a new entry are insert ts areautomatically update,
> but i would make the same on update ...
[snip]
> I try with a RULE but obtain only a loop, seem RULE aren't good to make
> such things, modify a statment on the same table it's related :(
>
> i look for a trigger but I suppose the same problem arise ...

No - a trigger is what you want. A rule is basically a macro - it transforms
the query, so you can end up with a loop.
If you use a BEFORE UPDATE trigger, you could update NEW.ts to always be up to
date.

Look for my "PostgreSQL Notes" on http://techdocs.postgresql.org/ - there's an
example of this in there somewhere (a bit out of date, but still should be
valid). Probably also looking for the "PostgreSQL cookbook" on the same site.

--
  Richard Huxton
  Archonet Ltd