The ReadData method displays the contents of the CategoryName column of the Categories table. We use it several times in the Main method to show the current status of the Categories table, which changes after each of the insert, update, and delete commands. Because of this, it is convenient to reuse to show you the effects after each method call.
A SqlCommand object allows you to query and send commands to a data base. It has methods that are specialized for different commands. The ExecuteReader method returns a SqlDataReader object for viewing the results of a select query. For insert, update, and delete SQL commands, you use the ExecuteNonQuery method. If you only need a single aggregate value from a query, the ExecuteScalar is the best choice.
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