title: Insert timestamp with timezone in query from C#
body: <p>I've the following table into my PostgreSQL database:</p>
  
  <pre><code>CREATE TABLE rates
  (
    source character varying(5) NOT NULL,
    target character varying(5) NOT NULL,
    "from" timestamp with time zone NOT NULL,
    "to" timestamp with time zone,
    exchange_rate numeric(10,10) NOT NULL,
  )
  </code></pre>
  
  <p>I've a text query with some placeholders for inserting a row into this table:</p>
  
  <pre><code>INSERT INTO public.rates 
        (source, target, from, to , exchange_rate)
  VALUES("{0}" , "{1}" , {2} , {3}, {4}          );
  </code></pre>
  
  <p>I don't know how I must replace placeholders <code>{2}</code> and <code>{3}</code> in order to give the correct timestamp with timezone.</p>
  
  <p>I need to put in <code>{2}</code> a custom <code>DateTime</code> with UTC timezone, that I specify, and in <code>{3}</code> the current time, always with UTC timezone.</p>
  
  <p>How I must replace these? Here's the code, where <code>"??"</code> are strings that I need to calculate:</p>
  
  <pre><code>string query = String.Format(AddExchangeQuery, "EUR", "USD", "??", "??", "3.2");
  NpgsqlCommand command = new NpgsqlCommand(query, connection);
  command.ExecuteScalar();
  </code></pre>