GroupAggregate  (cost=268287.50..304622.58 rows=854943 width=64) (actual time=2570.405..3141.006 rows=836894 loops=1)
   ->  Sort  (cost=268287.50..270424.86 rows=854943 width=64) (actual time=2570.393..2704.250 rows=836894 loops=1)
         Sort Key: iquiza.id, iquiz.id, iquiz.timeclose, iquiz.timelimit
         Sort Method:  external sort  Disk: 34376kB
         ->  Merge Left Join  (cost=38631.46..151908.24 rows=854943 width=64) (actual time=447.348..1580.284 rows=836894 loops=1)
               Merge Cond: ((iquiza.quiz = qogroup.quiz) AND (iquiza.userid = qogroup.userid))
               ->  Merge Join  (cost=2558.77..110823.81 rows=854943 width=64) (actual time=17.175..1015.331 rows=836894 loops=1)
                     Merge Cond: (iquiza.quiz = iquiz.id)
                     ->  Merge Left Join  (cost=36.04..93824.51 rows=854943 width=40) (actual time=0.492..678.636 rows=836894 loops=1)
                           Merge Cond: ((iquiza.quiz = quo.quiz) AND (iquiza.userid = quo.userid))
                           ->  Index Scan using mdl_quizatte_quiuseatt_uix on mdl_quiz_attempts iquiza  (cost=0.00..89509.40 rows=854943 width=24) (actual time=0.112..460.618 rows=836894 loops=1)
                           ->  Sort  (cost=36.04..37.43 rows=558 width=32) (actual time=0.377..0.540 rows=1545 loops=1)
                                 Sort Key: quo.quiz, quo.userid
                                 Sort Method:  quicksort  Memory: 64kB
                                 ->  Seq Scan on mdl_quiz_overrides quo  (cost=0.00..10.58 rows=558 width=32) (actual time=0.006..0.115 rows=558 loops=1)
                     ->  Sort  (cost=2038.38..2074.35 rows=14386 width=24) (actual time=16.657..79.949 rows=846675 loops=1)
                           Sort Key: iquiz.id
                           Sort Method:  quicksort  Memory: 1505kB
                           ->  Seq Scan on mdl_quiz iquiz  (cost=0.00..1044.86 rows=14386 width=24) (actual time=0.003..10.232 rows=14336 loops=1)
               ->  Sort  (cost=36072.70..36313.32 rows=96248 width=32) (actual time=430.170..430.170 rows=1 loops=1)
                     Sort Key: qogroup.quiz, qogroup.userid
                     Sort Method:  quicksort  Memory: 3082kB
                     ->  Subquery Scan qogroup  (cost=25218.59..28106.03 rows=96248 width=32) (actual time=377.773..390.918 rows=32966 loops=1)
                           ->  HashAggregate  (cost=25218.59..27143.55 rows=96248 width=48) (actual time=377.772..386.557 rows=32966 loops=1)
                                 ->  Merge Left Join  (cost=0.00..20578.71 rows=309325 width=48) (actual time=0.116..279.176 rows=294777 loops=1)
                                       Merge Cond: (gm.groupid = qgo1.groupid)
                                       ->  Merge Left Join  (cost=0.00..19791.97 rows=309325 width=40) (actual time=0.094..235.873 rows=294777 loops=1)
                                             Merge Cond: (gm.groupid = qgo2.groupid)
                                             ->  Merge Left Join  (cost=0.00..18992.75 rows=309325 width=32) (actual time=0.086..181.716 rows=294686 loops=1)
                                                   Merge Cond: (gm.groupid = qgo3.groupid)
                                                   ->  Merge Left Join  (cost=0.00..18166.63 rows=309325 width=24) (actual time=0.034..141.426 rows=294686 loops=1)
                                                         Merge Cond: (gm.groupid = qgo4.groupid)
                                                         ->  Index Scan using mdl_groumemb_gro_ix on mdl_groups_members gm  (cost=0.00..17377.23 rows=309325 width=16) (actual time=0.014..92.186 rows=294686 loops=1)
                                                         ->  Index Scan using mdl_quizover_gro_ix on mdl_quiz_overrides qgo4  (cost=0.00..35.16 rows=77 width=16) (actual time=0.018..0.035 rows=3 loops=1)
                                                               Filter: (qgo4.timelimit > 0)
                                                   ->  Index Scan using mdl_quizover_gro_ix on mdl_quiz_overrides qgo3  (cost=0.00..35.16 rows=2 width=16) (actual time=0.050..0.050 rows=1 loops=1)
                                                         Filter: (qgo3.timelimit = 0)
                                             ->  Index Scan using mdl_quizover_gro_ix on mdl_quiz_overrides qgo2  (cost=0.00..35.16 rows=390 width=16) (actual time=0.008..0.089 rows=258 loops=1)
                                                   Filter: (qgo2.timeclose > 0)
                                       ->  Index Scan using mdl_quizover_gro_ix on mdl_quiz_overrides qgo1  (cost=0.00..35.16 rows=8 width=24) (actual time=0.021..0.021 rows=1 loops=1)
                                             Filter: (qgo1.timeclose = 0)
 Total runtime: 3203.680 ms
(42 rows)