Thanks for the suggestions regarding non-printing characters, definitely
makes sense as a likely culprit!
However, the data really does seem to be identical in this case:
mysql> select id, customer_id, concat('-', group_id, '-') from
app_customergroupmembership where customer_id ='ajEiQA';
+-------------+-------------+----------------------------+
| id | customer_id | concat('-', group_id, '-') |
+-------------+-------------+----------------------------+
| 20279608258 | ajEiQA | -ddH6Ev- |
| 20279608269 | ajEiQA | -ddH6Ev- |
+-------------+-------------+----------------------------+
2 rows in set (0.00 sec)
I also ran the data through hexdump as a secondary check, also looks
identical:
mysql --defaults-extra-file=~/.customers_mysql.cnf app -s -e "select
id, customer_id, group_id from app_customergroupmembership where
customer_id ='ajEiQA';" | hexdump -c
0000000 2 0 2 7 9 6 0 8 2 5 8 \t a j E i
0000010 Q A \t d d H 6 E v \n 2 0 2 7 9 6
0000020 0 8 2 6 9 \t a j E i Q A \t d d H
0000030 6 E v \n
Any other suggestions given this info?
Thanks,
--
Chris Hornung
Johan De Meersman <mailto:vegiv...@tuxera.be>
March 24, 2015 at 6:08 AM
Please do
select id, customer_id, concat('-', group_id, '-')
from app_customergroupmembership
where customer_id ='ajEiQA';
I suspect one of those group IDs has a trailing space or similar 'invible'
character that makes it not identical.
----- Original Message -----
From: "Chris Hornung"<chris.horn...@klaviyo.com>
To: "MySql"<mysql@lists.mysql.com>
Sent: Monday, 23 March, 2015 18:20:36
Subject: duplicate rows in spite of multi-column unique constraint
Hello,
I'm come across a situation where a table in our production DB has a
relatively small number of duplicative rows that seemingly defy the
unique constraint present on that table.
We're running MySQL 5.6.19a via Amazon RDS. The table in question is
~250M rows.
`show create table` gives:
app_customergroupmembership | CREATE TABLE `app_customergroupmembership` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`customer_id` varchar(6) COLLATE utf8_bin NOT NULL,
`group_id` varchar(6) COLLATE utf8_bin NOT NULL,
`created` datetime NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `app_customergroupmembership_customer_id_31afe160_uniq`
(`customer_id`,`group_id`),
KEY `app_customergroupmembership_group_id_18aedd38e3f8a4a0`
(`group_id`,`created`)
) ENGINE=InnoDB AUTO_INCREMENT=21951158253 DEFAULT CHARSET=utf8
COLLATE=utf8_bin
Despite that, records with duplicate customer_id/group_id do exist:
mysql> select * from app_customergroupmembership where customer_id =
'ajEiQA';
+-------------+-------------+----------+---------------------+
| id | customer_id | group_id | created |
+-------------+-------------+----------+---------------------+
| 20279608258 | ajEiQA | ddH6Ev | 2015-02-17 00:14:54 |
| 20279608269 | ajEiQA | ddH6Ev | 2015-02-17 00:14:54 |
+-------------+-------------+----------+---------------------+
Interestingly, these dupe records can't seem to be queried when using
both columns from the unique constraint in the WHERE clause:
mysql> select * from app_customergroupmembership where customer_id =
'ajEiQA' and group_id = 'ddH6Ev';
+-------------+-------------+----------+---------------------+
| id | customer_id | group_id | created |
+-------------+-------------+----------+---------------------+
| 20279608258 | ajEiQA | ddH6Ev | 2015-02-17 00:14:54 |
+-------------+-------------+----------+---------------------+
Any thoughts on how this situation came to pass, and how to prevent it
from happening?
Thanks,
--
Chris Hornung
