What collation does MySQL use by default for ORDER BY? - mysql

Question

These queries both give the result I expect:
SELECT sex
FROM ponies
ORDER BY sex COLLATE latin1_swedish_ci ASC
SELECT sex
FROM ponies
ORDER BY CONVERT(sex USING utf8) COLLATE utf8_general_ci ASC
| f |
| f |
| m |
| m |
+---+
But this query gives a different result:
SELECT sex FROM ponies ORDER BY sex ASC
| m |
| m |
| f |
| f |
+---+
Here's the configuration:
SHOW VARIABLES LIKE 'collation\_%'
| collation_connection | utf8_general_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
+----------------------+-------------------+
The table collation is latin1_swedish_ci.
MySQL server is 5.5.16.

Answer 1

Table Collations
Collation defaults are stored on a table-by-table basis. There is a server-set default, but that is applied to the table at the time it is created.
To find the collation for a specific table, run this query:
SHOW TABLE STATUS LIKE 'ponies'\G
You should see output like this:
*************************** 1. row ***************************
Name: ponies
Engine: MyISAM
Version: 10
Row_format: Fixed
Rows: 8
Avg_row_length: 20
Data_length: 160
Max_data_length: 5629499534213119
Index_length: 1024
Data_free: 0
Auto_increment: NULL
Create_time: 2012-02-27 10:16:25
Update_time: 2012-02-27 10:17:40
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
And you can see the Collation setting in that result.
Column collations
You can also override collation settings on particular columns within a table. A create table statement like this would create a latin1_swedish_ci table, with a utf8_polish_ci column:
CREATE TABLE ponies (
sex CHAR(1) COLLATE utf8_polish_ci
) CHARACTER SET latin1 COLLATE latin1_swedish_ci;
The best way to view the results of this is like this:
SHOW FULL COLUMNS FROM ponies;
Output:
+-------+---------+----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+-------+---------+----------------+------+-----+---------+-------+---------------------------------+---------+
| sex | char(1) | utf8_polish_ci | YES | | NULL | | select,insert,update,references | |
+-------+---------+----------------+------+-----+---------+-------+---------------------------------+---------+
1 row in set (0.00 sec)

Answer 2

The documentation says it uses a case insensitive character comparison by default. I don't see why you are not getting that result though.
The documentation also suggests using the binary qualifier for case sensitive comparison. I wonder if that would affect your result?:
SELECT sex FROM ponies ORDER BY BINARY sex ASC

Answer 3

This behaviour can be observed when sex is an ENUM in which case it is usually sorted by the numerical position in the ENUM definition. Only when a collation is explicitly given an it is sorted in alphabetical order.