Обсуждение: database design questions

Hello,

I'm designing a  database and I'm having  some problems, so I  ask you a
suggestion.

1) The database I'm going to develop is  a big list with a catalog of
items and I  want to  store subsets  of this  list representing  the
available items in several places.

My idea  is to create the  big table with  all the elements and  then to
create another  table, where each  row holds a pair  (id_item, id_place)
and  thanks to  this create  several views,  joining the  two tables
and selecting the rows with a give id_place.

Do you think it's too heavy? Is there a simpler way to do it?

2) do you think it's possible in  a plpgsql procedure select the name of
a table into a variable and use that variable in the query?

I mean, can I do something like

SELECT INTO table_name get_table_name();
SELECT * FROM table_name;

?

3) faq 4.11.1 says

>    CREATE TABLE person (
>        id   SERIAL,
>        name TEXT
>    );
>
>is automatically translated into this:
>
>    CREATE SEQUENCE person_id_seq;
>    CREATE TABLE person (
>        id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
>        name TEXT
>    );

how can I do it with a INT8 instead of a INT4?

Thank you

--
Non c'è più forza nella normalità, c'è solo monotonia.

--- Tomi NA <hefest@gmail.com> wrote:

> On 4/3/06, Ottavio Campana <ottavio@campana.vi.it> wrote:
>
>
> > 3) faq 4.11.1 says
> >
> > >    CREATE TABLE person (
> > >        id   SERIAL,
> > >        name TEXT
> > >    );
> > >
> > >is automatically translated into this:
> > >
> > >    CREATE SEQUENCE person_id_seq;
> > >    CREATE TABLE person (
> > >        id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
> > >        name TEXT
> > >    );
> >
> > how can I do it with a INT8 instead of a INT4?
> >
> > Thank you
> >
>
> Is there a reason not to write explicitly?
>
> CREATE SEQUENCE person_id_seq;
> CREATE TABLE person (
> id   INT8 NOT NULL DEFAULT nextval('person_id_seq'),
> name TEXT
> );

you could also do:

    CREATE TABLE person (
        id   BIGSERIAL,
        name TEXT
    );


Regards,

Richard

on 4/3/06 7:38 AM, ottavio@campana.vi.it purportedly said:

> 1) The database I'm going to develop is  a big list with a catalog of
> items and I  want to  store subsets  of this  list representing  the
> available items in several places.
>
> My idea  is to create the  big table with  all the elements and  then to
> create another  table, where each  row holds a pair  (id_item, id_place)
> and  thanks to  this create  several views,  joining the  two tables
> and selecting the rows with a give id_place.
>
> Do you think it's too heavy? Is there a simpler way to do it?

On the surface, perhaps. Depending on your implementation details, you may
be adding unnecessary overhead. No one can really say since we don't know
what you are trying to accomplish.

> 2) do you think it's possible in  a plpgsql procedure select the name of
> a table into a variable and use that variable in the query?
>
> I mean, can I do something like
>
> SELECT INTO table_name get_table_name();
> SELECT * FROM table_name;

Yes, kind of. I.e., you can probably do what you want but not with the
syntax you are showing. See SELECT INTO and EXECUTE in chapter 36 of the
online docs.

> 3) faq 4.11.1 says
>
>>    CREATE TABLE person (
>>        id   SERIAL,
>>        name TEXT
>>    );
>>
>> is automatically translated into this:
>>
>>    CREATE SEQUENCE person_id_seq;
>>    CREATE TABLE person (
>>        id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
>>        name TEXT
>>    );
>
> how can I do it with a INT8 instead of a INT4?


Use BIGSERIAL instead.

Best,

Keary Suska
Esoteritech, Inc.
"Demystifying technology for your home or business"

Ottavio Campana wrote:
>>   CREATE TABLE person (
>>       id   SERIAL,
>>       name TEXT
>>   );

> how can I do it with a INT8 instead of a INT4?

Do you really expect that sequence to reach over 2 billion? Otherwise
I'd stick with the SERIAL, nothing wrong with that unless you're selling
electrons seperately or something like that (hmm... how much are they? I
sure could use a few extra).

--
Alban Hertroys
alban@magproductions.nl

magproductions b.v.

T: ++31(0)534346874
F: ++31(0)534346876
M:
I: www.magproductions.nl
A: Postbus 416
    7500 AK Enschede

// Integrate Your World //

Alban Hertroys wrote:
> Ottavio Campana wrote:
>>>   CREATE TABLE person (
>>>       id   SERIAL,
>>>       name TEXT
>>>   );
>
>> how can I do it with a INT8 instead of a INT4?
>
> Do you really expect that sequence to reach over 2 billion? Otherwise
> I'd stick with the SERIAL, nothing wrong with that unless you're selling

Depends on what the dynamics of his design are.  I.e. if he frequently
creates and deletes "people", then he can consume a lot of "id-space"
even though there aren't many real people in the database itself.

Personally, I doubt this is the case.  But, can see other applications
where this could be true.  Since you can't reuse old id's, it's easier
to just use a bigger size datum than having to worry how the database
will react when/if you run out of them!

> electrons seperately or something like that (hmm... how much are they? I
> sure could use a few extra).

Three for a quark...  keep the charge!  [sic] :>

--don

Alban Hertroys wrote:
> Ottavio Campana wrote:
>
>>>   CREATE TABLE person (
>>>       id   SERIAL,
>>>       name TEXT
>>>   );
>
>
>> how can I do it with a INT8 instead of a INT4?
>
>
> Do you really expect that sequence to reach over 2 billion? Otherwise
> I'd stick with the SERIAL, nothing wrong with that unless you're selling
> electrons seperately or something like that (hmm... how much are they? I
> sure could use a few extra).

I agree wih you, but I think that in the feature the could be more than
2 billions. I don't want to alter in the future the database

--
Non c'è più forza nella normalità, c'è solo monotonia.

hubert depesz lubaczewski wrote:
>     2) do you think it's possible in  a plpgsql procedure select the name of
>     a table into a variable and use that variable in the query?
> possible, but not really good way. read about 'execute' in plpgsql.

why isn't it good?

I mean, from my point of view is like a function accepting a pointer. In
many languages it is used.

--
Non c'è più forza nella normalità, c'è solo monotonia.