On 06/07/11 01:52, John Fabiani 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.
Johnf
Hi John,
How about using a table to hold the latest sequence for each order type
and date, along with a function to insert a new order?
(I've included the code to test the idea and the results, I am using
9.1beta2, but it should not make any difference - I think!):
DROP TABLE IF EXISTS my_order;
DROP TABLE IF EXISTS order_sequence;
CREATE TABLE my_order
(
order_num text PRIMARY KEY,
payload text
);
CREATE TABLE order_sequence
(
type int,
day date,
seq int NOT NULL,
PRIMARY KEY (type, day)
);
CREATE OR REPLACE FUNCTION create_my_order
(
IN type int,
IN day date,
IN payload text
) RETURNS VOID
AS
$$
DECLARE
v_order_num text;
v_seq_old int;
v_seq_new int;
BEGIN
SELECT
os.seq
FROM
order_sequence os
WHERE
os.type = create_my_order.type AND
os.day = create_my_order.day
INTO
v_seq_old;
IF v_seq_old IS NULL THEN
v_seq_new := 1;
INSERT INTO order_sequence(type, day, seq)
VALUES (type, day, v_seq_new);
ELSE
v_seq_new := v_seq_old + 1;
UPDATE
order_sequence AS os
SET
seq = v_seq_new
WHERE
os.type = create_my_order.type AND
os.day = create_my_order.day;
END IF;
v_order_num := type::text ||
'-' ||
to_char(day, 'YYMMDD') ||
'-' ||
v_seq_new::text;
INSERT INTO my_order(order_num, payload)
VALUES (v_order_num, payload);
END;
$$ LANGUAGE plpgsql
VOLATILE
;
SELECT create_my_order (0, '2010-03-24', 'order #1 details');
SELECT create_my_order (0, '2010-03-24', 'order #2 details');
SELECT create_my_order (0, '2010-06-15', 'order #3 details');
SELECT create_my_order (5, '2010-03-24', 'order #4 details');
SELECT create_my_order (0, '2010-06-15', 'order #5 details');
SELECT create_my_order (3, '2010-06-14', 'order #6 details');
TABLE order_sequence;
TABLE my_order;
////////// This outputs the following:
type | day | seq
------+------------+-----
0 | 2010-03-24 | 2
5 | 2010-03-24 | 1
0 | 2010-06-15 | 2
3 | 2010-06-14 | 1
(4 rows)
order_num | payload
------------+------------------
0-100324-1 | order #1 details
0-100324-2 | order #2 details
0-100615-1 | order #3 details
5-100324-1 | order #4 details
0-100615-2 | order #5 details
3-100614-1 | order #6 details
(6 rows)
