PostgreSQL Anonymous Code Block Database Migration

migration.sql

-- PostgreSQL database migration to split up one table into two smaller ones and store the new ID with the original table

DO $$
    DECLARE
      -- vars
      insert_id int;
    BEGIN
      -- do something

      FOR r IN
        -- fetch all slots
        SELECT tournament_id, user_id FROM tournament_slots
      LOOP
        -- create event party
        INSERT INTO event_parties (squad_id) VALUES (NULL) 
          RETURNING id INTO insert_id;
        RAISE NOTICE 'insert_id (%)', insert_id;

        -- insert into event party members
        INSERT INTO event_party_members 
          (event_party_id, user_id, payment_id, 
            join_timestamp, checkin_timestamp)
          SELECT insert_id, r.user_id, payment_id, 
            join_timestamp, checkin_timestamp
          FROM tournament_slots 
          WHERE user_id = r.user_id 
            AND tournament_id = r.tournament_id;

        -- update original record
        UPDATE tournament_slots 
          SET event_party_id = insert_id
          WHERE user_id = r.user_id
            AND tournament_id = r.tournament_id;
        RAISE NOTICE '.';
        
      END LOOP;
      RETURN;
    END$$;