fix state_group_events count query

SQL-for-analyzing-Synapse-PostgreSQL-database-stats.md

@@ -18,9 +18,9 @@ SELECT r.name, s.room_id, s.current_state_events
 
 and by state_group_events count:
 ```
-SELECT 's.room_id', count('s.room_id') cnt, 'rs.name' FROM state_groups_state s
-LEFT JOIN room_stats_current rs USING (room_id)
-GROUP BY s.room_id        
+SELECT rss.name, s.room_id, count(s.room_id) FROM state_groups_state s
+LEFT JOIN room_stats_state rss USING (room_id)
+GROUP BY s.room_id, rss.name        
 ORDER BY count(s.room_id) DESC
 LIMIT 20;
 ```