ADO.NET Provider for Greenplum

Build 21.0.7930

Querying with the DataReader

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

Using the GreenplumDataReader

The GreenplumDataReader retrieves data faster than the GreenplumDataAdapter because it can retrieve data in pages. As you read data from the GreenplumDataReader, 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 "template1"."public".Orders table:

C#

string connectionString = "User=user;Password=admin;Database=dbname;Server=127.0.0.1;Port=5432";

using (GreenplumConnection connection = new GreenplumConnection(connectionString)) {
  GreenplumCommand cmd = new GreenplumCommand("SELECT * FROM \"template1\".\"public\".Orders", connection);
  
  GreenplumDataReader rdr = cmd.ExecuteReader();

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

VB.NET

Dim connectionString As String = "User=user;Password=admin;Database=dbname;Server=127.0.0.1;Port=5432"

Using connection As New GreenplumConnection(connectionString)
  Dim cmd As New GreenplumCommand("SELECT * FROM \"template1\".\"public\".Orders", connection)

  Dim rdr As GreenplumDataReader = cmd.ExecuteReader()

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

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Build 21.0.7930