The CData ADO.NET Provider for Apache Impala implements two ADO.NET interfaces you can use to retrieve data from Apache Impala: ApacheImpalaDataAdapter and ApacheImpalaDataReader objects. Whereas ApacheImpalaDataAdapter objects retrieve a single result set of all the data that matches a query, ApacheImpalaDataReader objects fetch data in subset increments as needed.

Using the ApacheImpalaDataReader

The ApacheImpalaDataReader retrieves data faster than the ApacheImpalaDataAdapter because it can retrieve data in pages. As you read data from the ApacheImpalaDataReader, it periodically requests the next page of results from the data source, if required. This causes results to be returned at a faster rate. The following example selects all the columns from the [CData].[Default].Customers table:

C#

string connectionString = "Server=127.0.0.1;Port=21050;";

using (ApacheImpalaConnection connection = new ApacheImpalaConnection(connectionString)) {
  ApacheImpalaCommand cmd = new ApacheImpalaCommand("SELECT * FROM [CData].[Default].Customers", connection);
  
  ApacheImpalaDataReader rdr = cmd.ExecuteReader();

  while (rdr.Read()) {
    Console.WriteLine(String.Format("\t{0} --> \t\t{1}", rdr["City"], rdr["CompanyName"]));
  }
}

VB.NET

Dim connectionString As String = "Server=127.0.0.1;Port=21050;"

Using connection As New ApacheImpalaConnection(connectionString)
  Dim cmd As New ApacheImpalaCommand("SELECT * FROM [CData].[Default].Customers", connection)

  Dim rdr As ApacheImpalaDataReader = cmd.ExecuteReader()

  While rdr.Read()
    Console.WriteLine([String].Format(vbTab & "{0} --> " & vbTab & vbTab & "{1}", rdr("City"), rdr("CompanyName")))
  End While
End Using