generate sequential reference numbers - php

Question

I am generating sequential reference numbers like complaint/1, complaint/2 when an insertion is made. I get what the previously generated value is (complaint/2) and then increment.
But when two users submit at the same time, I sometimes get same reference nos for both complaints.
How do I prevent this?
SELECT RIGHT(Date_format(from_financial_year_,'%Y'),2),
RIGHT(Date_format(to_financial_year_,'%Y'),2)
INTO from_financial_year_,
to_financial_year_;SELECT rec.receipt_ref_no
INTO last_receipt_ref_num_
FROM svk_apt_receipts rec
WHERE Replace(Substring_index(rec.receipt_ref_no, '/', 2),'REC/','') = Concat(from_financial_year_,to_financial_year_)
AND rec.customer_id = customer_id_
AND rec.association_id = association_id_
ORDER BY rec.receipt_id DESC limit 1;IF(last_receipt_ref_num_ IS NULL) then
SELECT 1
INTO max_ref_id_;
else
SELECT (replace(last_receipt_ref_num_, concat('REC/',from_financial_year_,to_financial_year_,'/'),'')+1)
INTO max_ref_id_;ENDIF;SELECT Concat('REC/',from_financial_year_,to_financial_year_,'/',max_ref_id_)
INTO receipt_ref_no_;INSERT INTO svk_apt_receipts
(
receipt_ref_no, paid, payable, is_paid, master_receipt_to_id, receipt_from_id, receipt_to_id, receipt_date,
receipt_mode, transaction_ref_no, customer_id, association_id, is_active, created_by, created_on, receipt_status_id, remarks
)
VALUES
( receipt_ref_no_, _total_amount, 0,1,3, receipt_from_id_, receipt_to_id_, Cast(Now()AS DATE), 3, _transaction_ref_no,
customer_id_, association_id_, 1, _created_by, Now(), 2, 'Paid through Payment Gateway'
);

Answer 1

As mentioned in comments, just store an autoincrementing id. All the other stuff can be handled by trivial queries and/or your presentation layer.
By way of example...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id SERIAL PRIMARY KEY
,user INT NOT NULL
);
INSERT INTO my_table (user) VALUES
(1),(1),(3),(3),(5),(2),(1),(8),(4),(5),(7),(5),(5),(4),(1),(2),(3),(6),(4),(6),(1),(5),(1),(8);
SELECT * FROM my_table;
+----+------+
| id | user |
+----+------+
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 3 |
| 5 | 5 |
| 6 | 2 |
| 7 | 1 |
| 8 | 8 |
| 9 | 4 |
| 10 | 5 |
| 11 | 7 |
| 12 | 5 |
| 13 | 5 |
| 14 | 4 |
| 15 | 1 |
| 16 | 2 |
| 17 | 3 |
| 18 | 6 |
| 19 | 4 |
| 20 | 6 |
| 21 | 1 |
| 22 | 5 |
| 23 | 1 |
| 24 | 8 |
+----+------+
24 rows in set (0.01 sec)
SELECT x.*
, COUNT(*) complaint
FROM my_table x
JOIN my_table y
ON y.user = x.user
AND y.id <= x.id
GROUP
BY x.id
ORDER
BY user
, id;
+----+------+-----------+
| id | user | complaint |
+----+------+-----------+
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 7 | 1 | 3 |
| 15 | 1 | 4 |
| 21 | 1 | 5 |
| 23 | 1 | 6 |
| 6 | 2 | 1 |
| 16 | 2 | 2 |
| 3 | 3 | 1 |
| 4 | 3 | 2 |
| 17 | 3 | 3 |
| 9 | 4 | 1 |
| 14 | 4 | 2 |
| 19 | 4 | 3 |
| 5 | 5 | 1 |
| 10 | 5 | 2 |
| 12 | 5 | 3 |
| 13 | 5 | 4 |
| 22 | 5 | 5 |
| 18 | 6 | 1 |
| 20 | 6 | 2 |
| 11 | 7 | 1 |
| 8 | 8 | 1 |
| 24 | 8 | 2 |
+----+------+-----------+
24 rows in set (0.00 sec)