Re: Function PostgreSQL 9.2
On Tue, May 3, 2016 at 5:53 PM, Adrian Klaver <adrian.klaver@aklaver.com> wrote:
On 05/03/2016 02:27 PM, drum.lucas@gmail.com wrote:
On 4 May 2016 at 01:18, Melvin Davidson <melvin6925@gmail.com
<mailto:melvin6925@gmail.com>> wrote:
On Tue, May 3, 2016 at 1:21 AM, David G. Johnston
<david.g.johnston@gmail.com <mailto:david.g.johnston@gmail.com>> wrote:
Well.. I don't need to add a constraint if I already have a
default value, that's right...
Wrong
David J.
What you need is a TRIGGER function & TRIGGER that will select and
assign the next users_code based on company_id.
I'm not going to write the whole thing for you, but here is part of
the trigger function logic.
eg: IF NEW.company_id = 1 THEN
NEW.users_code = NEXTVAL(c1_users_code_seq);
ELSEIF NEW.company.id <http://NEW.company.id> = 2 THEN
NEW.users_code = NEXTVAL(c2_users_code_seq);
ELSEIF NEW.company.id <http://NEW.company.id> = 3 THEN
NEW.users_code = NEXTVAL(c3_users_code_seq);
...
...
ELSE
< something bad happened because NEW.company_id was
not valid ?
END IF;
Do I have to have one sequence peer company_id ? There will be
thousands.. isn't there a better way to do that?
A sequence just keeps on incrementing. If you want a gapless sequence for each company that each increment independently of each other then yes you will need a separate sequence for each.
For an alternate strategy see this related thread:
http://www.postgresql.org/message-id/2926B083-33C9-4648-8635-BC293C70ED45@ravnalaska.net
in particular this link from the thread:
http://www.postgresql.org/message-id/44E376F6.7010802@seaworthysys.com--
Seriously, get yourself the books I have recommended and study them
BEFORE you continue attempting to design your database.
You need a firm understanding of logical design & flow, otherwise
you will be wasting your time.
That's what I'm doing.. Studying.. asking for some help to get a better
understand.... isn't this the purpose of this mail list?
Adrian Klaver
adrian.klaver@aklaver.com
>Do I have to have one sequence peer company_id ? There will be thousands.. isn't there a better way to do that?
I agree that having thousands of sequences can be hard to manage,
especially in a function, but you did not state that fact before,
only that you wanted separate sequences for each company. That
being said, here is an alternate solution.
1. CREATE TABLE company_seqs
(company_id bigint NOT NULL,
last_seq bigint NOT NULL,
CONSTRAINT company_seqs_pk PRIMARY KEY (company_id)
);
2. Every time you create a new company, you must insert the
corresponding company_id and last_seq [which will be 1}
into the company_seqs table.
3. Change the trigger function logic to something like below:
DECLARE
v_seq_num INTEGER;
BEGIN
SELECT last_seq
FROM company_seqs
WHERE company_id = NEW.company_id INTO v_seq_num;
UPDATE company_seqs
SET last_seq = last_seq + 1
WHERE company_id = NEW.company_id;
new.users_code = v_seq_num;
Now, just a quick comment. As has been said before, wanting a sequence with no gaps for
each user in each company is a bit unrealistic and serves no purpose. For example,
company_id 3 has 10 users, 1 > 10. What do you do when user 3 leaves and is deleted?
As long as you have a unique user_code for each user, it does not matter.
>... Studying.. asking for some help to get a better understand.... isn't this the purpose of this mail list?
Yes, but at the same time, it is evident that you are trying to design the database before you have
a valid understanding of database design. To wit, you are putting the cart before the horse.
While this list is here to help you, it is not meant as a DATABASE 101 course.
--
Melvin Davidson
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
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