C# 一个Form内 在chart控件中，当点击A按钮，显柱图，点击B按钮，显折线图
求高手们给予帮助
private void btnColumn_Click(object sender, EventArgs e)
  {
   
   
  SqlConnection conn = new SqlConnection();
  conn.ConnectionString = "Server=;database=;Uid=;Pwd=;";
  conn.Open();
  SqlCommand cmd = new SqlCommand();
  cmd.CommandText = "select * from 电压寿命关系"; cmd.Connection = conn;
  SqlDataReader read = cmd.ExecuteReader();
   
  chart1.DataBindTable(read, "电压(V)");
  conn.Close();
   
   
  }

  private void btnLine_Click(object sender, EventArgs e)
  {
   
  SqlConnection conn = new SqlConnection();
  conn.ConnectionString = "Server=;database=;Uid=;Pwd=;";
  conn.Open();
  SqlCommand cmd = new SqlCommand();
  cmd.CommandText = "select * from 电压寿命关系"; cmd.Connection = conn;
  SqlDataReader read = cmd.ExecuteReader();
   
  chart1.DataBindTable(read, "电压(V)");
  chart1.Series["寿命"].ChartType = SeriesChartType.Line;
   
  }
我想当我点击某按钮时会显示不同图像，但报错已有一个相同名称的Serie存在，不知怎么办？

------解决方案--------------------
清空Serie试看。