note on aggregate

postgres/aggregate.md

@@ -1,3 +1,8 @@
+To extract aggregate definitions can select from `pg_aggregate`
+
+
+SQL for current aggregates I'm using now:
+```      
 CREATE OR REPLACE FUNCTION public.jsonb_concat(
     state jsonb,
     concat jsonb)
@@ -40,4 +45,5 @@ CREATE AGGREGATE public.jsonb_obj_aggc(jsonb) (
   SFUNC=public.jsonb_concat,
   STYPE=jsonb,
   INITCOND='{}'
-);
+);
+```