w_user表结构如下:
+--------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------+------+-----+---------+----------------+
| u_id | int(4) | NO | PRI | NULL | auto_increment |
| u_name | char(8) | YES | | NULL | |
| u_pass | char(8) | YES | | NULL | |
| u_img | blob | YES | | NULL | |
| u_info | text | YES | | NULL | |
+--------+---------+------+-----+---------+----------------+
以下创建索引的语句正确的是( )