On Tue, Jul 5, 2011 at 6:52 AM, John Fabiani
<johnf@jfcomputer.com> wrote:
Hi,
I have a special need to create a sequence like function.
"O-20110704 -2" which is
"O" for order (there are other types)
"20110704" is for July 4, 2011
'2' the second order of the day for July 4, 2011
I of course can get the type and date. What I don't know is how to get is the
last number. It would seem to be that I would need a loop to determine if the
next number existed.
LOOP
--Check to see if the string exist in a table
-- count = count +1
-- until I don't find the string
END LOOP;
but then I thought I could do something like
for $1 in (select string from sometable)
LOOP
count = count + 1
or something like this
for i in 1..999 LOOP
-- check for the existence of the string in a table using 'i'
-- there will never be 999 orders in one day.
END LOOP
So here is the question what would be the best way for a multi-user system?
If someone has a better thought - it would be helpful.
BTW I did NOT design the number - in fact it seems silly to me.
I'd probably do the following. Create a table to hold the current date as a string appropriate for use in ids. I'd also create a sequence for each of the id types. I'd set up a cron job (or equivalent) to run at midnight which updates the date and resets all of the sequences to 1 within a transaction. You can probably do all of it in a single query.
Then I'd do inserts which generate the id by concatenating the type initial with the date and a sequence, probably in an insert trigger on the table if you are ok with server generated ids. Otherwise, you could do insert with a subquery which generates the id:
insert into order (id, x, y) values ((select 'O-' || d.datestring || '-' || nextval('order_id_sequence') from date_table d), 'x_value', 'y_value');
If you are using hibernate or some other ORM, you can surely use an insert trigger to generate the id and tell the ORM to use a server generated id.
