You can access the same column information about the results of a query that you can for table schemas. See Columns for the columns returned.

Retrieving Result Set Metadata

You can use the GetSchemaTable method of the ExcelOnlineDataReader to retrieve result set metadata. Call GetSchemaTable after calling ExecuteReader.

Each row of the DataTable describes a column in the query's result.

C#

string connectionString = "InitiateOAuth=GETANDREFRESH;";

using (ExcelOnlineConnection conn = new ExcelOnlineConnection(connectionString)) {
  ExcelOnlineCommand cmd = new ExcelOnlineCommand("SELECT * FROM Test_xlsx_Sheet1 WHERE Column2 = 'Bob'", conn);
  ExcelOnlineDataReader rdr = cmd.ExecuteReader();
  DataTable schemaTable = rdr.GetSchemaTable();
  foreach (DataRow row in schemaTable.Rows) {
    foreach (DataColumn col in schemaTable.Columns) {
      Console.WriteLine("{0}: {1}", col.ColumnName, row[col]);
    }
  }
}

VB.NET

Dim connectionString As String = "InitiateOAuth=GETANDREFRESH;"

Using conn As New ExcelOnlineConnection(connectionString)
  Dim cmd As New ExcelOnlineCommand("SELECT * FROM Test_xlsx_Sheet1 WHERE Column2 = 'Bob'", conn)
  Dim rdr As ExcelOnlineDataReader = cmd.ExecuteReader()
  Dim schemaTable As DataTable = rdr.GetSchemaTable()
  For Each row As DataRow In schemaTable.Rows
    For Each col As DataColumn In schemaTable.Columns
      Console.WriteLine("{0}: {1}", col.ColumnName, row(col))
    Next
  Next
End Using