c# - 为什么我提供数据时数据库却添加空值？

Question

我正在 textbox1 和 dropdown1 中插入数据，但数据仅保存在写入第二个位置的查询中“即本例中的 c_name”。 C_name 为空或插入空值。

protected void Button1_Click(object sender, EventArgs e)
{
    con.Open();
    MySqlCommand cmd = con.CreateCommand();

    cmd.CommandType = CommandType.Text;

    cmd.CommandText = "insert into market (m_name) values ('" + TextBox1.Text + "')";
    cmd.CommandText = "insert into city (c_name) values('" + DropDownList1.SelectedValue + "')";

    if (DropDownList1.SelectedValue == "-1")
    {
        Response.Write("Please select a city");
    }


    cmd.ExecuteNonQuery();
    con.Close();
}

Answer 1

您应该在第一个 cmd.CommandText 之后执行 cmd.ExecuteNonQuery()，然后您必须对第二个 cmd.CommandText 执行相同的操作>，两个查询都将执行其操作。

protected void Button1_Click(object sender, EventArgs e)
{
   if (DropDownList1.SelectedValue == "-1")
   {
       Response.Write("Please select a city");
       return; // Must return don't execute after 'if' part or use 'else' there
   }

   con.Open();
   MySqlCommand cmd = con.CreateCommand();

   cmd.CommandType = CommandType.Text;

   cmd.CommandText = "insert into market (m_name) values ('" + TextBox1.Text + "')";

   cmd.ExecuteNonQuery(); // First insert executed here

   cmd.CommandText = "insert into city (c_name) values('" + DropDownList1.SelectedValue + "')";

   cmd.ExecuteNonQuery(); // Second insert executed here
   con.Close();
}