Below is the documentation for DataReader on the MSDN website.
You use the Read method of the DataReader object to obtain a row from the results of the query. You can access each column of the returned row by passing the name or ordinal reference 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,
see the OleDbDataReader Class and the SqlDataReader Class. Using the typed accessor methods, when the underlying data type is known, reduces the amount of type conversion required when retrieving the column value.
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