using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var text = "ISNULL(d.Type, 0), d.Subject + ', ' + d.Name, d.Something,array_position(ARRAY['f', 'p', 'i', 'a']::varchar[], x_field), test";
		var pattern = @"(\([^()]*\)|'[^']*')|\s*,";
    	var result = Regex.Replace(text, pattern, m => m.Groups[1].Success ? m.Value : " DESC,");
       	Console.WriteLine(result);
	}
}