Add convert decimal (#29)

* Add convertation from clickhouse decimal type

Co-authored-by: Алексей Редькин <[email protected]>

lib/pillar/type_convert/to_elixir.ex

@@ -90,4 +90,8 @@ defmodule Pillar.TypeConvert.ToElixir do
            ] and is_number(value) do
     value
   end
+
+  def convert("Decimal" <> _decimal_subtypes, value) do
+    value
+  end
 end

test/pillar_test.exs

@@ -270,6 +270,22 @@ defmodule PillarTest do
                })
     end
 
+    test "Decimal test", %{conn: conn} do
+      create_table_sql = """
+        CREATE TABLE IF NOT EXISTS decimal_table (field Decimal64(2)) ENGINE = Memory
+      """
+
+      insert_query_sql = """
+        INSERT INTO decimal_table VALUES (500000.05)
+      """
+
+      assert {:ok, ""} = Pillar.query(conn, create_table_sql)
+      assert {:ok, ""} = Pillar.query(conn, insert_query_sql)
+
+      assert {:ok, [%{"field" => 500_000.05}]} =
+               Pillar.select(conn, "SELECT * FROM decimal_table LIMIT 1")
+    end
+
     test "Float tests", %{conn: conn} do
       sql = ~s(
         SELECT