Pro C# 2010 and the .NET 4 Platform, Fifth Edition

21.10. Building a Reusable Data Access Library

The ExecuteReader() method extracts a data reader object that allows you to examine the results of a SQL Select statement using a forward-only, read-only flow of information. However, when you wish to submit SQL statements that result in the modification of a given table (or any other non-query SQL statement, such as creating tables or granting permissions), you call the ExecuteNonQuery() method of your command object. This single method performs inserts, updates, and deletes based on the format of your command text.

NOTE

Technically speaking, a nonquery is a SQL statement that does not return a result set. Thus, Select statements are queries, while Insert, Update, and Delete statements are not. ...