add example3: postgres implemented

example3/snowflake-id.sql

@@ -0,0 +1,37 @@
+CREATE SEQUENCE public.global_id_seq;
+ALTER SEQUENCE public.global_id_seq OWNER TO postgres;
+
+CREATE OR REPLACE FUNCTION public.id_generator()
+    RETURNS bigint
+    LANGUAGE 'plpgsql'
+AS $BODY$
+DECLARE
+    our_epoch bigint := 1314220021721;
+    seq_id bigint;
+    now_millis bigint;
+    -- the id of this DB shard, must be set for each
+    -- schema shard you have - you could pass this as a parameter too
+    shard_id int := 1;
+    result bigint:= 0;
+BEGIN
+    SELECT nextval('public.global_id_seq') % 1024 INTO seq_id;
+
+    SELECT FLOOR(EXTRACT(EPOCH FROM clock_timestamp()) * 1000) INTO now_millis;
+    result := (now_millis - our_epoch) << 23;
+    result := result | (shard_id << 10);
+    result := result | (seq_id);
+	return result;
+END;
+$BODY$;
+
+ALTER FUNCTION public.id_generator() OWNER TO postgres;
+
+create schema shard_1
+create table users(
+  id bigint not null default id_generator(),
+  email varchar(255) not null unique,
+  first varchar(50),
+  last varchar(50)
+);
+
+-- select id_generator();