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SqlDataReader Usage and Example:
To retrieve data using a DataReader, create an instance of the Command object, and then create a DataReader by calling Command.ExecuteReader to retrieve rows from a data source. The DataReader provides an unbuffered stream of data that allows procedural logic to efficiently process results from a data source sequentially.
The following example illustrates using a DataReader, where reader represents a valid DataReader and command represents a valid Command object.
reader = command.ExecuteReader();

Use the DataReader.Read method to obtain a row from the query results. You can access each column of the returned row by passing the name or ordinal number of the column to the DataReader. However, for best performance, the DataReader provides a series of methods that allow you to access column values in their native data types (GetDateTime, GetDouble, GetGuid, GetInt32, and so on). For a list of typed accessor methods for data provider-specific DataReaders, see SqlDataReader. Using the typed accessor methods when you know the underlying data type reduces the amount of type conversion required when retrieving the column value.
The SqlDataReader class is used to read data from a SQL Server database in a forward-only manner. It inherits from the DbDataReader class and implements the IDisposable interface. The SqlDataReader provides properties and methods to read data from the database, such as GetString, GetInt32, and Read(). To populate a SqlDataReader, the ExecuteReader method of the SqlCommand object is called after executing a query against a SQL database.