SqlCommand

This type deals with databases. It executes SQL commands on a database. It sends an SQL command to a database that is specified by an SqlConnection object.

We then call instance methods to physically apply the command to the database. We use a SELECT TOP command text, and also ORDER BY.

Example

This program uses the SqlCommand data object in C#. We use SqlCommand in the context of a complete but trivial program that reads data from a specific database on the disk.

using System;
using System.Data.SqlClient;

class Program
{
    static void Main()
    {
        //
        // The program accesses the connection string.
        // ... It uses it on a connection.
        //
        string conString = ConsoleApplication1.Properties.Settings.Default.ConnectionString;
        using (SqlConnection connection = new SqlConnection(conString))
        {
            connection.Open();
            //
            // SqlCommand should be created inside using.
            // ... It receives the SQL statement.
            // ... It receives the connection object.
            // ... The SQL text works with a specific database.
            //
            using (SqlCommand command = new SqlCommand("SELECT TOP 3 * FROM Dogs1 ORDER BY Weight", connection))
            {
                //
                // Instance methods can be used on the SqlCommand.
                // ... These read data.
                //
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        for (int i = 0; i < reader.FieldCount; i++)
                        {
                            Console.WriteLine(reader.GetValue(i));
                        }
                        Console.WriteLine();
                    }
                }
            }
        }
    }
}
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Using

The SQL data objects are wrapped in a resource acquisition statement. This ensures that resources are properly acquired and disposed of when no longer needed.

Constructor

The call to the SqlCommand constructor uses 2 parameters. The first parameter is the actual SQL source text. This string uses SQL and is not compiled by the C# compiler.

A summary

We wrote a complete program that reads from a database on the local disk. The SqlCommand has a constructor. You can specify its connection and the SQL text.