YIIではフィールドリストの列「id」があいまいです

どちらか

変更：$criteria->select = "username" to ==> $criteria->select = "u.username"

または

削除：$criteria->alias = "u" and change $criteria->select = "username" to ==> $criteria->select = "t.username" and change all left join alias 'u.field_name' to ==> 't.field_name'