CREATE SCHEMA business
  AUTHORIZATION postgres;

CREATE TABLE business."Contact"
(
  "ID" bigint NOT NULL,
  first_name character varying(100),
  last_name character varying(100),
  extended json,
  niss character varying(11),
  CONSTRAINT "Contact_pkey" PRIMARY KEY ("ID")
)
WITH (
  OIDS=FALSE
);
ALTER TABLE business."Contact"
  OWNER TO postgres;

<packages>
  <package id="CsvHelper" version="2.15.0.0" targetFramework="net45" />
  <package id="Newtonsoft.Json" version="9.0.1-beta1" targetFramework="net45" />
  <package id="Npgsql" version="3.1.4" targetFramework="net45" />
</packages>

    public static void ImportContact(string filePath)
    {
        using (var reader = File.OpenText(filePath))
        {
            NpgsqlConnection conn = new 
                NpgsqlConnection
               ("Server=127.0.0.1;Port=5432;UserId=postgres;Password=SECRET;Database=yourdb");

            try
            {
                conn.Open();
                var csv = new CsvReader(reader);
                while (csv.Read())
                {
                    var seq = csv.GetField<int>("seq");
                    var first = csv.GetField<string>("first");
                    var last = csv.GetField<string>("last");
                    var age = csv.GetField<int>("age");
                    var street = csv.GetField<string>("street");
                    var city = csv.GetField<string>("city");
                    var state = csv.GetField<string>("state");
                    var zip = csv.GetField<string>("zip");
                    var birthday = csv.GetField<string>("birthday");
                    var domain = csv.GetField<string>("pick");
                    var gender = csv.GetField<string>("gender");
                    var phone = csv.GetField<string>("phone");
                    var niss1 = new Random().Next(500101, 999999);
                    var niss2 = new Random().Next(11111, 99999);
                    string niss = niss1.ToString() + niss2.ToString();

                    var streetNumber = 1;
                    IFormatProvider culture = new System.Globalization.CultureInfo("fr-FR", true);
                    var birthdayeAsdate = Convert.ToDateTime(birthday, culture);
                    var email = $"{first}.{last}@{domain}";

                    Contact c = new Contact()
                    {
                        Street = street,
                        StreetNumber = streetNumber,
                        City = city,
                        State = state,
                        Zip = zip,
                        Age = age,
                        BirthDay = birthdayeAsdate,
                        Gender = gender,
                        Phone = phone,
                        Email = email
                    };

                    var serialized = Ser(c);
                    var query = $"insert into business.\"Contact\"( \"ID\", first_name, last_name, niss, extended) values({seq}, '{first}', '{last}', '{niss}','{serialized}' )";

                    NpgsqlCommand cmd = new NpgsqlCommand(query, conn);
                    cmd.ExecuteNonQuery();
                }
            }
            finally
            {
                conn?.Close();
            }
        }
    }

    public static string Ser(object obj)
    {
        using (var stringWriter = new StringWriter())
        {
            using (var writer = new JsonTextWriter(stringWriter)
            {
                //add some options if needed
            })
            {
                new JsonSerializer { NullValueHandling = NullValueHandling.Ignore }.Serialize(writer, obj);
            }
            var res = stringWriter.ToString();

            return res;
        }
    }

}

public class Contact
{
    public Int32? Id { get; set; }
    public String FirstName { get; set; }
    public String LastName { get; set; }
    public Int32? Age { get; set; }
    public String Street { get; set; }
    public String City { get; set; }
    public String State { get; set; }
    public String Zip { get; set; }
    public Int32? StreetNumber { get; set; }
    public String Email { get; set; }
    public String Phone { get; set; }
    public DateTime? BirthDay { get; set; }
    public String Gender { get; set; }
}

-----------------
-- simple select
----------------
SELECT "ID", extended->>'Zip' as zip FROM business."Contact" limit 100;
--field type json (no index):13ms
--field type jsonb 
--no index : 12ms
--with gin index : 12ms
--with indexes on email and zip : 12ms

-----------------
-- select with cast to int and greater then
----------------
SELECT "ID", extended->>'Zip' as zip, extended->>'Email' as email  FROM business."Contact"
WHERE CAST(extended->>'Zip' AS integer) > 2000
Order by zip desc
limit 100
--field type json (no index) : 9267ms
--field type jsonb 
--no index : 1731ms
--with gin index : 1837ms
--with indexes on email and zip : 13ms

-----------------
-- select with cast to int and greater then
----------------
SELECT "ID", extended->>'Zip' as zip, extended->>'Email' as email  FROM business."Contact"
WHERE (extended->>'Zip')::int > 2000
Order by zip desc
limit 100
--field type json (no index):9278
--field type jsonb 
--no index : 1634ms
--with gin index : 1822ms
--with indexes on email and zip : 14ms

-----------------
-- select containment
----------------
SELECT "ID", extended->>'Zip' as zip, extended->>'Email' as email  FROM business."Contact"
WHERE extended @> '{"Email": "Harriett.Thornton@twitter.com"}'
--field type json (no index) : does not support containment -> @>
--field type jsonb 
--no index : 623ms
--with gin index : 12ms
--with indexes on email and zip : 13ms

-----------------
-- select with like
----------------
SELECT "ID", extended->>'Zip' as zip, extended->>'Email' as email  FROM business."Contact"
WHERE extended->>'Email' Like '%W%' AND (extended->>'Zip')::int > 2000
order by email desc limit 100
--field type json (no index):4130ms
--field type jsonb 
--no index 1014ms
--with gin index : 1073ms
--with indexes on email and zip : 13ms

-----------------
--Index creation
-----------------
-- change to jsonb
ALTER TABLE business."Contact"
  ALTER COLUMN extended
  SET DATA TYPE jsonb
  USING extended::jsonb;
-- Gin 
CREATE INDEX extended_data_gin ON business."Contact" USING GIN (extended);
-- index on field zip
CREATE INDEX ON business."Contact" ((extended->>'Zip'));
-- index on field email
CREATE INDEX ON business."Contact" ((extended->>'Email'));