Getting one data from another table in DropownList with AutoPostBack

I have a Customer table --> CustomerNumber and CustomerName columns

I have a Sales table --> CustomerName columns

I have a Label (represent CustomerNumber) and a DropDownList (represent CustomerName)

I getting to DropDownList Sales table --> CustomerName with SqlDataSource.

I want automaticly (with AutoPostBack) filling Label with CustomerNumber which CustomerName selected in DropDownList

Example SQL:

开发者_如何转开发select A.CustomerNumber from Customer A, Sales B where B.CustomerName = DropDownList1.SelectedItems.Value

I'm thinking like this.

How can i do that?

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

---

Try this

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
if(-1 != DropDownList1.SelectedIndex)
{
using(SqlConnection connection = new SqlConnection("connectionString"))
{
connection.Open();
using(SqlCommand command = new SqlCommand("SELECT A.CUSTOMERNUMBER FROM CUSTOMER A, SALES B WHERE B.CUSTOMERNAME = @CustomerName"))
{
command.Connection = connection;
command.Parameters.AddWithValue("@CustomerName", DropDownlist1.SelectedValue.ToString());
this.Label1.Text = command.ExecuteScalar().ToString();
}
}
}
}

Hope it works. Disclaimer : I didn't tested the code

---

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)

{

 string selectedName = DropDownList1.SelectedValue;

 string sqlQuery = "select A.CustomerNumber from Customer A, Sales B where B.CustomerName = '" + DropDownList1.SelectedValue + "'";
 // pass you sql query to command object and call execute scalar method
 label1.Text = dbCommand.ExecuteScalar().ToString();

}

What do ExecuteScalar do?