using System;

using System.Text.RegularExpressions;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string simplequery=@" select c.id,person_id,c.customer_no,c.status,p.first_name,p.last_name,p.dob as DateOfBirth

                        from customer c 

                        inner join person p on p.id=c.person_id";

        string query=@" select c.id,person_id,c.customer_no,c.status,p.first_name,p.last_name,p.dob as DateOfBirth,concat(p.first_name,' ',p.last_name) as fullName

                        from customer c 

                        inner join person p on p.id=c.person_id";

        string[] IgnoredFields = new string[]{"id", "person_id","DateOfBirth"};

         query = Regex.Replace(query, @"\t|\n|\r", ""); // remove new line character

​

            var reg=new Regex(@"(?is)SELECT(.*?)(?<!\w*"")FROM(?!\w*?"")(.*?)(?=WHERE|ORDER|$)");

            var columns=reg.Match(query).Groups[1].Value.Split(new char[]{','},StringSplitOptions.RemoveEmptyEntries);

            var fieldsSubString = String.Join(",", columns); // taking string in between select and from keyword

​

            fieldsSubString=Regex.Replace(fieldsSubString, @"(\(|[\s]?(concat\(|min\(|max\(|count\())(.*?)(\)(.*?)([\s|as\s]+))", ""); //remove manipulated columns

            var commaSeperatedFields=fieldsSubString.Trim(',').Replace(",,", ","); // remove unwanted commas 

            var fieldsWithAlias=commaSeperatedFields.Split(','); 

            var fields=fieldsWithAlias.Select(x=>(x.Contains(".")?x.Split('.')[1]:x));

            fields=fields.Select(x=>(x.Contains(" as ")?x.Split(new string[] { " as " }, StringSplitOptions.None)[1]:x));

            var remains = fields.Except(IgnoredFields);

        var customQuery=@"select "+String.Join(",",remains)+" from ("+query+") xc2ty" ;

        Console.WriteLine(customQuery);

    }

}