Reading SQL Server database using datasource

The SqlDataSource is intended as what the name implies - a data source for data binding. It is not a way to get individual values from a database table.

If you need to read a single value, you should use straight ADO.NET - SqlConnection and SqlCommand - to read that value - something like:

string sqlStmt = "SELECT FirstName FROM dbo.YourTable WHERE ID = @ID";

using(SqlConnection conn = new SqlConnection(your-connection-string-here-))
using(SqlCommand cmd = new SqlCommand(sqlStmt, conn))
{
   cmd.Parameters.Add("@ID", SqlDbType.Int).Value = 4044;

   conn.Open();
   string firstName = cmd.ExecuteScalar().ToString(); 
   conn.Close();
}

The ExecuteScalar call works only if you want to read a single row, single column value - like here. Otherwise you need to use either the SqlDataReader, or use the DataTable and a SqlDataAdapter to fill that data table (if you have multiple rows).

Update: if you want to use a SqlDataAdapter instead - do this:

public DataTable LoadData()
{
   DataTable result = new DataTable();

   string sqlStmt = "SELECT ID, FirstName, LastName, Country " + 
                    "FROM dbo.YourTable";

   using(SqlConnection conn = new SqlConnection(your-connection-string-here-))
   using(SqlCommand cmd = new SqlCommand(sqlStmt, conn))
   {
       SqlDataAdapter dap = new SqlDataAdapter(cmd);
       dap.Fill(result);
   }

   return result;
}

When you call this method, you'll get back a DataTable that contains the columns you've defined in your SQL statement, and all rows from the database table.

DataTable myData = LoadData();

Now, you can iterate over the rows and get the FirstName value for each row:

foreach(DataRow row in myData.Rows)
{
     string firstName = row["FirstName"].ToString();
     // do whatever you need to do with the first name
}