Discuz! Database Error

(1267) Illegal mix of collations (gbk_chinese_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='
SELECT * FROM common_member WHERE username='İ'

PHP Debug

No.FileLineCode
1home.php41require_once(%s)
2source/module/home/home_space.php30table_common_member->fetch_by_username(%s)
3source/class/table/table_common_member.php65discuz_database::fetch_first(%s, Array)
4source/class/discuz/discuz_database.php94discuz_database::query(%s, Array, false, false)
5source/class/discuz/discuz_database.php142db_driver_mysql->query(%s, false, false)
6source/class/db/db_driver_mysql.php152db_driver_mysql->halt(%s, %d, %s)
7source/class/db/db_driver_mysql.php223break()
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