Postgresql - Using subqueries with alter sequence expressions

I don't believe you can do it like that but you should be able to use the setval function direction which is what the alter does.

select setval('sequenceX', (select max(table_id)+1 from table), false)

The false will make it return the next sequence number as exactly what is given.

In addition if you have mixed case object names and you're getting an error like this:

ERROR: relation "public.mytable_id_seq" does not exist

... the following version using regclass should be useful:

select setval('"public"."MyTable_Id_seq"'::regclass, (select MAX("Id") FROM "public"."MyTable"))