Is this a MySQL sorting bug?

5
votes

I was faced with strange server behavior MySQL 5.1.50. It sorts records incorrectly.

For example I have created a table test:

CREATE TABLE IF NOT EXISTS `test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(250) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;


INSERT INTO `test` (`id`, `title`) VALUES
(1, 'record1'),
(2, 'record2'),
(3, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'),
(4, 'ABCDEFGHIJKLMNOPQRSTUVWXYY');

and make an query:

mysql> set names utf8; Query OK, 0 rows affected (0.00 sec)

mysql> select * from test order by title asc;

+----+----------------------------+
| id | title                      |
+----+----------------------------+
|  3 | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
|  4 | ABCDEFGHIJKLMNOPQRSTUVWXYY |
|  1 | record1                    |
|  2 | record2                    |
+----+----------------------------+

4 rows in set (0.00 sec)

mysql> select * from test order by title desc;

+----+----------------------------+
| id | title                      |
+----+----------------------------+
|  2 | record2                    |
|  1 | record1                    |
|  3 | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
|  4 | ABCDEFGHIJKLMNOPQRSTUVWXYY |
+----+----------------------------+

4 rows in set (0.00 sec)

As you see records 3 and 4 don't change places

I did such query and some letters does not change an order, for example, A and a.

mysql> SELECT * FROM test ORDER BY title COLLATE utf8_unicode_ci ASC;

+----+---------+
| id | title   |
+----+---------+
|  1 | A       |
| 27 | a       |
| 28 | b       |
|  2 | B       |
| 29 | c       |
|  3 | C       |
|  4 | D       |
| 30 | d       |
| 31 | e       |
|  5 | E       |
|  6 | F       |
| 32 | f       |
| 33 | g       |
|  7 | G       |
| 34 | h       |
|  8 | H       |
| 35 | i       |
|  9 | I       |
| 36 | j       |
| 10 | J       |
| 11 | K       |
| 37 | k       |
| 12 | L       |
| 38 | l       |
| 39 | m       |
| 13 | M       |
| 40 | n       |
| 14 | N       |
| 41 | o       |
| 15 | O       |
| 42 | p       |
| 16 | P       |
| 17 | Q       |
| 43 | q       |
| 44 | r       |
| 18 | R       |
| 19 | S       |
| 45 | s       |
| 20 | T       |
| 46 | t       |
| 21 | U       |
| 47 | u       |
| 48 | v       |
| 22 | V       |
| 49 | w       |
| 23 | W       |
| 50 | x       |
| 24 | X       |
| 25 | Y       |
| 51 | y       |
| 26 | Z       |
| 52 | z       |
+----+---------+

mysql> SELECT * FROM test ORDER BY title COLLATE utf8_unicode_ci DESC;

+----+---------+
| id | title   |
+----+---------+
| 52 | z       |
| 26 | Z       |
| 25 | Y       |
| 51 | y       |
| 50 | x       |
| 24 | X       |
| 49 | w       |
| 23 | W       |
| 48 | v       |
| 22 | V       |
| 47 | u       |
| 21 | U       |
| 20 | T       |
| 46 | t       |
| 45 | s       |
| 19 | S       |
| 18 | R       |
| 44 | r       |
| 17 | Q       |
| 43 | q       |
| 16 | P       |
| 42 | p       |
| 41 | o       |
| 15 | O       |
| 40 | n       |
| 14 | N       |
| 39 | m       |
| 13 | M       |
| 12 | L       |
| 38 | l       |
| 11 | K       |
| 37 | k       |
| 10 | J       |
| 36 | j       |
|  9 | I       |
| 35 | i       |
|  8 | H       |
| 34 | h       |
|  7 | G       |
| 33 | g       |
| 32 | f       |
|  6 | F       |
|  5 | E       |
| 31 | e       |
|  4 | D       |
| 30 | d       |
| 29 | c       |
|  3 | C       |
|  2 | B       |
| 28 | b       |
|  1 | A       |
| 27 | a       |
+----+---------+

I think that it is the bug with collation.

May be someone ran into such conduct of server?

3
mysqlsorting
Your setup works as expected for me in 5.0.77. I didn't find any verification on Google but it looks like a bug to me – Cfreak
My local v5.1.41 works fine, too. – mindas
@mindas What kind of collation do you have? – Cristian Boariu
@Christian: latin1_swedish_ci (Ubuntu default) – mindas
I did an update with an alphabet in the first message – adre

3 Answers

1
votes

Seems to be a bug in your version indeed.

I tried it with MySQL 5.5.8 and there it's sorted correctly:

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.5.8 MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> select * from test order by title asc;
+----+----------------------------+
| id | title                      |
+----+----------------------------+
|  4 | ABCDEFGHIJKLMNOPQRSTUVWXYY |
|  3 | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
|  1 | record1                    |
|  2 | record2                    |
+----+----------------------------+
4 rows in set (0.00 sec)

mysql> select * from test order by title desc;
+----+----------------------------+
| id | title                      |
+----+----------------------------+
|  2 | record2                    |
|  1 | record1                    |
|  3 | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
|  4 | ABCDEFGHIJKLMNOPQRSTUVWXYY |
+----+----------------------------+
4 rows in set (0.00 sec)

mysql>
1
votes

What happens if you try?:

SELECT *
FROM test
ORDER BY title ASC
COLLATE utf8_unicode_ci;

Have you tried this:

INSERT INTO test (id, title)
VALUES
(101, 'A'),
(102, 'B'),
(103, 'C'),
...
(126, 'Z');

SELECT *
FROM test
ORDER BY title ASC
;

To see if the problem (or bug) is related to long strings or to collation?

0
votes

Since you have mixtures of text and numerical values, you might try to sort like this:

mysql> select * from test order by length(title), title;

as described here.

[If that doesn't work, you may be able to replace the second instance of title with asc or desc as desired]