帖，vc#sql编程出有关问题了，各位大神

求助帖，vc#sql编程出问题了，求助各位大神
private void button3_Click(object sender, EventArgs e)
  {
  if (textBox1.Text.Trim() == "")
  {
  MessageBox.Show("请输入学号!");
  return;
  }
  SqlConnection conn = new SqlConnection(strcon);
  string sqlStr = "update [chengjiguanli] set";
  if (textBox2.Text.Trim().ToString() != "") //如果姓名有输入
  { sqlStr += "[xm]='" + textBox2.Text.Trim() + "',"; }
  if (textBox3.Text.Trim() != "") //如果教师名有输入
  { sqlStr += "[jsm]='" + textBox3.Text.Trim() + "',"; }
  if (textBox4.Text.Trim() != "") //如果课程名称有输入
  { sqlStr += "[kcmc]='" + textBox4.Text.Trim() + "',"; }
  if (textBox5.Text.Trim() != "") //如果分数有输入
  { sqlStr += "[fs]='" + textBox5.Text.Trim() + "',"; }
  if (textBox6.Text.Trim() != "") //如果状态有输入
  { sqlStr += "[zt]='" + textBox6.Text.Trim() + "',"; }
  if (FileNamePath != "") //如果选择了照片
  { sqlStr += "[zp]=@zp,"; }
  sqlStr += "[kclx]='" + comboBox1.Text + "',";
  sqlStr += " where xh='" + textBox1.Text.Trim() + "'";
  SqlCommand cmd = new SqlCommand(sqlStr, conn);
  if (FileNamePath != "") //如果选择了照片
  {
  FileStream fs = null;
  fs = new FileStream(FileNamePath, FileMode.Open, FileAccess.Read);
  MemoryStream mem = new MemoryStream();
  byte[] data1 = new byte[fs.Length];
  fs.Read(data1, 0, (int)fs.Length);
  cmd.Parameters.Add("@zp", SqlDbType.VarBinary); //这里选择VarBinary类型  
  cmd.Parameters["@zp"].Value = data1; //把照片变化成字节数组
  }
  try
  {
  conn.Open();
  int yxh = cmd.ExecuteNonQuery();
  if (yxh == 1) //如果受影响的行数为1则修改成功
  { MessageBox.Show("修改成功"); }
  else
  { MessageBox.Show("数据库中没有此学生！"); }
  this.chengjiguanliTableAdapter.Fill(this.fATEDataSet.chengjiguanli);
  }
  catch (Exception ex)
  { MessageBox.Show("出错，没有完成成绩的修改！" + ex.Message); }
  finally
  {
  conn.Close();
  FileNamePath = "";
  }

  }



程序运行后会出现“出错，没有完成成绩的修改！关键字‘where’附近有语法错误“的提示
我检查不出来错误，求助各位大神。。。

------解决方案--------------------
sqlStr += "[kclx]='" + comboBox1.Text + "',";
改为
sqlStr += "[kclx]='" + comboBox1.Text + "' ";