C#

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

public class Program
{
	public static void Main()
	{
		string strID = "10010";
		Dictionary<string, string> g = new Dictionary<string, string>();
		g.Add("K", "k1");
		g.Add("L", "l1");
		string updateCustomerIncome = string.Format("  update CustomerIncome set {0} where ID = '{1}'; ",
                    string.Join(", ", g.Select(x => String.Format("{0} = '{1}'", x.Key, x.Value))), strID);
		Console.WriteLine(updateCustomerIncome);
		
		//var result2 = string.Join(", ", g.Select(x => String.Format("{0} = '{1}'", x.Key, x.Value)));
		//Console.WriteLine(result2);
		
		//Console.WriteLine(string.Join(", ", new List<string>(g.Keys)));
		//Console.WriteLine(string.Join(", ", new List<string>(g.Values)));
		string insertCustomerIncome = string.Format("  insert CustomerIncome(ID, {0}) values ('{1}', '{2}');", 
					string.Join(", ", new List<string>(g.Keys)), strID, string.Join("', '", new List<string>(g.Values)));
		Console.WriteLine(insertCustomerIncome);
		
		StringBuilder sb = new StringBuilder();	
		sb.AppendFormat("if exists (select * from CustomerIncome where id = '{0}')", strID);
		sb.AppendLine();
		sb.AppendLine(updateCustomerIncome);
		sb.AppendLine("else");
		sb.Append(insertCustomerIncome);
		
		Console.WriteLine(sb.ToString());
	}
}

the output

  update CustomerIncome set K = 'k1', L = 'l1' where ID = '10010'; 
  insert CustomerIncome(ID, K, L) values ('10010', 'k1', 'l1');
if exists (select * from CustomerIncome where id = '10010')
  update CustomerIncome set K = 'k1', L = 'l1' where ID = '10010'; 
else
  insert CustomerIncome(ID, K, L) values ('10010', 'k1', 'l1');

references:
https://dotnetfiddle.net/uiFWXo
How to get the list of key in dictionary