using System;

using System.Data.SqlClient;

​

public class SqlActions

{

    SqlConnection connection;

    public SqlActions()

    {

        connection = new SqlConnection("Server = serverName; Database = customerData; Uid = userId; Pwd = password");   

    }

    public SqlActions(string connectionString)

    {

        connection = new SqlConnection(connectionString);   

    }

    public void ReadData(string databaseCommand)

    {       

        try

        {

            connection.Open();

            SqlCommand command = new SqlCommand(databaseCommand, connection);

            using(SqlDataReader reader = command.ExecuteReader())

            {

                while(reader.Read())

                {

                    Console.WriteLine(reader[0]);   

                }

            }

​

        }

        finally

        {

            if (connection != null)

                connection.Close(); 

        }   

    }

    public void WriteData(string databaseCommand)

    {

        try

        {

            connection.Open();

            SqlCommand command = new SqlCommand(databaseCommand, connection);

            command.ExecuteNonQuery();

        }

        finally

        {

            if (connection != null)

                connection.Close();

        }

    }

    public void ReadFirstEntry(string databaseCommand)

    {

        try

        {

            connection.Open();

            SqlCommand command = new SqlCommand(databaseCommand, connection);

            command.ExecuteScalar();

        }

        finally

        {

            if (connection != null)

                connection.Close();

        }

    }

}

public class Program

{

    public static void Main()

    {

        SqlActions sqlCustomers = new SqlActions();

        SqlActions sqlPreferences = new SqlActions("Server = serverName; Database = preferencesData; Uid = userId; Pwd = password;");

        sqlCustomers.ReadData("SELECT Name, City FROM Customers");

        sqlCustomers.WriteData("INSERT INTO Cusomers(Name, City) VALUES ('Alex','Denver')");

        sqlPreferences.ReadFirstEntry("SELECT count(*) FROM Preferences(delivery)");

    }

}