Every once in a while I write a MySQL query that fails because of differing collations. Here’s how to resolve those issues.
First, a little background.
You can see what character sets and collations your server has like so:
mysql> show character set;
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
+----------+-----------------------------+---------------------+--------+
mysql> show collation like 'latin1%';
+-------------------+---------+----+---------+----------+---------+
| Collation | Charset | Id | Default | Compiled | Sortlen |
+-------------------+---------+----+---------+----------+---------+
| latin1_german1_ci | latin1 | 5 | | Yes | 1 |
| latin1_swedish_ci | latin1 | 8 | Yes | Yes | 1 |
| latin1_danish_ci | latin1 | 15 | | Yes | 1 |
| latin1_german2_ci | latin1 | 31 | | Yes | 2 |
| latin1_bin | latin1 | 47 | | Yes | 1 |
| latin1_general_ci | latin1 | 48 | | Yes | 1 |
| latin1_general_cs | latin1 | 49 | | Yes | 1 |
| latin1_spanish_ci | latin1 | 94 | | Yes | 1 |
+-------------------+---------+----+---------+----------+---------+
FYI, the _ci, _cs and _bin endings indicate “case insensitive”, “case sensitive” and “binary”, respectively. Binary is, perforce, case sensitive.
To see the default settings for your server, check out the variables:
mysql> show variables like 'char%';
+--------------------------+------------------------------------------------------+
| Variable_name | Value |
+--------------------------+------------------------------------------------------+
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /Applications/xampp/xamppfiles/share/mysql/charsets/ |
+--------------------------+------------------------------------------------------+
8 rows in set (0.01 sec)
mysql> show variables like 'coll%';
+----------------------+-------------------+
| Variable_name | Value |
+----------------------+-------------------+
| collation_connection | latin1_swedish_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
+----------------------+-------------------+
3 rows in set (0.00 sec)
So, you can specify the character set and collation right down to the column. A collation is specific to a given character set, so you can’t compare two fields from different character sets, or from different collations. In fact, that’s where we started: MySQL rapped my knuckles for trying to compare fields with different collations.
Let’s set up a collation collision for demonstration purposes.
drop table if exists a;
create table a (
flda1 varchar(255)
) engine=myisam collate=latin1_swedish_ci;
drop table if exists b;
create table b (
fldb1 varchar(50) not null
) engine=myisam collate=latin1_general_ci;
insert into a values ('aaa');
insert into b values ('bbb');
So if we did a select comparing the two fields, we’d get:
mysql> select * from a, b where a.flda1 = b.fldb1;
ERROR 1267 (HY000): Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (latin1_general_ci,IMPLICIT) for operation '='
mysql>
Great. Now, to fix it, we want to set the collation of table b to latin1_swedish_ci. You’ll note that getting a “show create table b”, produces the following DDL script:
CREATE TABLE `b` (
`fldb1` varchar(50) collate latin1_general_ci NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci
Clearly we’ll need to change both the table and the field’s collations:
alter table b
character set latin1 collate latin1_swedish_ci,
modify column fldb1 varchar(50) character set latin1 collate latin1_swedish_ci NOT NULL
CREATE TABLE `b` (
`fldb1` varchar(50) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1
And now, when we execute the select script:
mysql> select * from a, b where a.flda1 = b.fldb1;
Empty set (0.20 sec)
