c# 必须声明标量变量@ 可是已经声明了啊

string number = txt_number.Text;
string name = txt_name.Text;
string mail = txt_mail.Text;
string pwd = txt_pwd.Text;
string sex = Convert.ToString("");
if (rb_boy.Checked)
{ sex = "男"; }
else
{ sex = "女"; }
string college = cmb_college.Text;
string major = cmb_major.Text;
string call = txt_call.Text;
string filepath = txt_filename.Text.Trim();
FileStream fs = new FileStream(filepath, FileMode.Open, FileAccess.Read);
byte[] file = new byte[fs.Length];
fs.Read(file, 0, (int)fs.Length);
fs.Close();
// string sql = string.Format("insert into customer values('{0}','{1}','{2}','{3}','{4}','{5}','{6}','{7}',@photo)", number, name, pwd, mail, sex, call, college, major);
string sql1 = string.Format("select count(*) from customer where number={0}",txt_number.Text);
string sql = "insert into commodity values(@photo,@number, @name,@ pwd, @mail,@sex,@call, @college,@major)";
SqlCommand com = new SqlCommand(sql1, DBhelper.con);
// com.Parameters.Add("@photo", SqlDbType.Image).Value =file ;
com.Parameters.AddWithValue("@photo", file);
com.Parameters.AddWithValue("@number", number);
com.Parameters.AddWithValue("@name", name);
com.Parameters.AddWithValue("@pwd", pwd);
com.Parameters.AddWithValue("@mail", mail);
com.Parameters.AddWithValue("@sex", sex);
com.Parameters.AddWithValue("@call", call);
com.Parameters.AddWithValue("@college", college);
com.Parameters.AddWithValue("@major", major);
if (txt_mail.Text.Length == 0 || txt_name.Text.Length == 0 || txt_number.Text.Length == 0 ||
txt_pwd.Text.Length == 0 || rb_boy.Checked == false && rb_girl.Checked == false ||
cmb_college.Text.Length == 0 || cmb_major.Text.Length == 0 || txt_call.Text.Length == 0)
{
MessageBox.Show("信息不完整！");
}
else
try
{
DBhelper.con.Open();
int i = (Int32)com.ExecuteScalar();
if (i > 0) //判断该学号是否注册过
{
MessageBox.Show("此学号已存在！");
txt_number.Text = "";
txt_number.Focus();
}
else
{
com.CommandText = sql;
i = com.ExecuteNonQuery();
MessageBox.Show("添加学生信息成功！");
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
finally
{ DBhelper.con.Close(); }