CREATE TABLE IF NOT EXISTS customers
(
 id INT NOT NULL GENERATED BY DEFAULT AS IDENTITY,
 name TEXT NOT NULL,
 referred_by INT,
 CONSTRAINT customers_pkey PRIMARY KEY (id),
 FOREIGN KEY (referred_by) REFERENCES customers (id)
);

INSERT INTO customers (name, referred_by) VALUES ('John Doe', null);
INSERT INTO customers (name, referred_by) VALUES ('Jane Smith', null);
INSERT INTO customers (name, referred_by) VALUES ('Anne Jenkins', 2);
INSERT INTO customers (name, referred_by) VALUES ('Eric Branford', null);
INSERT INTO customers (name, referred_by) VALUES ('Pat Richards', 1);
INSERT INTO customers (name, referred_by) VALUES ('Alice Barnes', 2);

SELECT COUNT(*) FROM customers WHERE referred_by <> 2;

public void Test()
{
    try
    {
        var cToken = new CancellationToken(canceled: true);

        Task.Run(() => Delay(cToken)).Wait();

        Console.Write("Completed");
    }
    catch (OperationCanceledException)
    {
        Console.Write("OperationCanceledException");
    }
    catch (AggregateException)
    {
        Console.Write("AggregateException");
    }
    catch (Exception)
    {
        Console.Write("Exception");
    }
}

private Task Delay(CancellationToken cToken)
{
    cToken.ThrowIfCancellationRequested();

    return Task.Delay(1000);
}

public void Test()
{
    try
    {
        var serviceProvider = new ServiceCollection()
            .AddScoped<INameProvider, NameProvider>()
            .AddSingleton<INameProvider, NameProvider2>()
            .BuildServiceProvider();

        var nameProvider = serviceProvider
            .CreateScope()
            .ServiceProvider
            .GetService<INameProvider>();

        Console.Write(nameProvider?.GetName() ?? "Null");
    }
    catch (Exception)
    {
        Console.Write("Exception");
    }
}

interface INameProvider
{
    string GetName();
}

class NameProvider : INameProvider
{
    public string GetName() => "Name";
}

class NameProvider2 : INameProvider
{
    public string GetName() => "Name2";
}

public void Test()
{
    var strEqual = (object)"14.01.2024" == (object)"14.01.2024";
    var dtEquals = (object)DateTime.Today == (object)DateTime.Today;
    var intEquals = (object)14012024 == (object)14012024;

    Console.Write($"{strEqual} {dtEquals} {intEquals}");
}

public void Test()
{
    try
    {
        var fullDay = TimeSpan.Parse("24:00:00");

        var days = fullDay.Days;
        var hours = fullDay.Hours;

        Console.Write($"{days}d {hours}h");
    }
    catch (Exception)
    {
        Console.Write("Exception");
    }
}

public class Increment
{
    private int _counter;

    public void Test()
    {
        Write(_counter++);
        Console.Write(_counter);
    }

    private void Write(int i)
    {
        Console.Write(i);
        Console.Write(_counter);
    }
}