EXPLAIN ANALYSE
SELECT u.id FROM mdl_user u JOIN(
        SELECT DISTINCT 
                eu20_u.id 
        FROM 
                mdl_user eu20_u 
        JOIN mdl_user_enrolments ej20_ue ON 
                ej20_ue.userid = eu20_u.id 
        JOIN mdl_enrol ej20_e ON (
                ej20_e.id = ej20_ue.enrolid 
                AND ej20_e.courseid = 16085
        ) 
        JOIN mdl_role_assignments eu19_ra3 ON (
                eu19_ra3.userid = eu20_u.id 
                AND eu19_ra3.roleid IN (5) 
                AND eu19_ra3.contextid IN (1,3,472391,546512)
        )
        JOIN mdl_groups_members gm18_gm ON (
                gm18_gm.userid = eu20_u.id 
                AND gm18_gm.groupid = 35335
        ) 
        WHERE 1 = 1 AND (eu20_u.id <> 1) AND eu20_u.deleted = 0
) je ON 
        je.id = u.id 
WHERE 
        u.deleted = 0 
ORDER 
        BY u.lastname, u.firstname, u.id;

                                                                                               QUERY PLAN                                                                                               
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=30.62..30.63 rows=1 width=23) (actual time=0.248..0.248 rows=4 loops=1)
   Sort Key: u.lastname, u.firstname, u.id
   Sort Method: quicksort  Memory: 25kB
   ->  Nested Loop  (cost=26.56..30.61 rows=1 width=23) (actual time=0.225..0.231 rows=4 loops=1)
         ->  HashAggregate  (cost=26.27..26.28 rows=1 width=8) (actual time=0.222..0.223 rows=4 loops=1)
               Group Key: eu20_u.id
               ->  Nested Loop  (cost=1.85..26.27 rows=1 width=8) (actual time=0.056..0.217 rows=4 loops=1)
                     ->  Nested Loop  (cost=1.56..25.94 rows=1 width=16) (actual time=0.043..0.118 rows=32 loops=1)
                           ->  Nested Loop  (cost=1.14..24.75 rows=1 width=24) (actual time=0.036..0.068 rows=4 loops=1)
                                 ->  Nested Loop  (cost=0.84..20.60 rows=1 width=16) (actual time=0.030..0.051 rows=4 loops=1)
                                       ->  Index Scan using mdl_groumemb_gro_ix on mdl_groups_members gm18_gm  (cost=0.42..9.47 rows=4 width=8) (actual time=0.011..0.011 rows=4 loops=1)
                                             Index Cond: (groupid = 35335)
                                       ->  Index Only Scan using mdl_roleassi_useconrol_ix on mdl_role_assignments eu19_ra3  (cost=0.42..2.77 rows=1 width=8) (actual time=0.008..0.008 rows=1 loops=4)
                                             Index Cond: ((userid = gm18_gm.userid) AND (roleid = 5))
                                             Filter: (contextid = ANY ('{1,3,472391,546512}'::bigint[]))
                                             Rows Removed by Filter: 7
                                             Heap Fetches: 7
                                 ->  Index Scan using mdl_user_id_pk on mdl_user eu20_u  (cost=0.29..4.13 rows=1 width=8) (actual time=0.004..0.004 rows=1 loops=4)
                                       Index Cond: (id = eu19_ra3.userid)
                                       Filter: ((id <> 1) AND (deleted = 0))
                           ->  Index Scan using mdl_userenro_use_ix on mdl_user_enrolments ej20_ue  (cost=0.42..1.06 rows=13 width=16) (actual time=0.003..0.011 rows=8 loops=4)
                                 Index Cond: (userid = eu20_u.id)
                     ->  Index Scan using mdl_enro_id_pk on mdl_enrol ej20_e  (cost=0.29..0.32 rows=1 width=8) (actual time=0.003..0.003 rows=0 loops=32)
                           Index Cond: (id = ej20_ue.enrolid)
                           Filter: (courseid = 16085)
                           Rows Removed by Filter: 1
         ->  Index Scan using mdl_user_id_pk on mdl_user u  (cost=0.29..4.31 rows=1 width=23) (actual time=0.002..0.002 rows=1 loops=4)
               Index Cond: (id = eu20_u.id)
               Filter: (deleted = 0)
 Planning time: 682.850 ms
 Execution time: 0.351 ms
(31 rows)