feature #4: create function for constitution and title (not article in title)

resources/functions/constitution/find_constitution_titles_by_id.sql

@@ -0,0 +1,20 @@
+create or replace function find_constitution_titles_by_id(in constitution_id uuid, out resource json) language plpgsql as
+$$
+declare
+    _constitution_id alias for constitution_id;
+begin
+    select json_agg(t)
+    from (
+        select
+            ti.id,
+            ti.name,
+            ti.rank
+        into resource
+        from title as ti
+        where ti.constitution_id = _constitution_id
+        order by ti.rank
+    ) as t;
+end;
+$$;
+
+-- drop function if exists find_constitution_titles_by_id(uuid, out json);