他の接続は問題無いのに，なぜか
Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '=':
などと言われるときは，character-set/collation を確認．
mysql> SHOW VARIABLES LIKE '%character%';
+--------------------------+----------------------------------------+
| Variable_name | Value |
+--------------------------+----------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql/share/mysql/charsets/ |
+--------------------------+----------------------------------------+
8 rows in set (0.00 sec)
mysql> SHOW VARIABLES LIKE '%collation%';
+----------------------+-----------------+
| Variable_name | Value |
+----------------------+-----------------+
| collation_connection | utf8_general_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+----------------------+-----------------+
3 rows in set (0.00 sec)
問題あるようなら下記を追加．
[mysqld]
default-character-set=utf8
character-set-server=utf8
collation-server=utf8_general_ci
[mysql]
default-character-set=utf8
