WLE participants in previous years

SQL

use commonswiki_p;

SELECT CONCAT("# {{#target:User_talk:", actor_name, "}}") as line
FROM revision r_prev
join categorylinks on rev_page = cl_from
join actor on rev_actor = actor_id and actor_user is not null
WHERE rev_parent_id = 0
and cl_to IN (
   "Images_from_Wiki_Loves_Monuments_2019_in_the_United_Kingdom"
) and not exists (
  SELECT 1
	FROM revision
	join categorylinks on rev_page = cl_from
	WHERE 
                  rev_parent_id = 0 AND  
                  rev_actor = r_prev.rev_actor	and 
                  cl_to IN ("Images_from_Wiki_Loves_Monuments_2010_in_the_United_Kingdom")  
)  
 GROUP BY actor_name
SQL

Checking query status...
