C#使用DataGridView控件显示数据表查询内容出现如下问题

Question

如上图所示，执行SQL查询语句后，控件会显示额外的空白列。请问这是怎么回事？
相关代码如下：
private SqlDataAdapter da = new SqlDataAdapter () ;
private DataSet sd = new DataSet("school");
string sql = "select 姓名,性别,职位,员工编号,部门编号,部门名称 from chaxun";
string connstring = @"Data Source =.\Sqlserver; Initial Catalog = school;Integrated Security=true ";
//创建连接
SqlConnection conn = new SqlConnection(connstring);
//打开链接
conn.Open();
SqlCommand comm = new SqlCommand(sql,conn);
da.SelectCommand = comm;
SqlCommandBuilder builder = new SqlCommandBuilder(da);
da.Fill(sd, "chaxun");
dgvCoures.DataSource = sd.Tables["chaxun"];
conn.Close();
}

Answer 1

da.Fill(sd, "chaxun");
dgvCoures.Columns.Clear();
dgvCoures.DataSource = sd.Tables["chaxun"];