Postgres 9.6

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CREATE TABLE T (seller_id int, payment_id varchar(3), payment_time timestamp, second_diff int);
    
INSERT INTO T (seller_id, payment_id, payment_time, second_diff)
VALUES
    (1, 'pl',  '2015-01-08 09:23:04', 151),
    (1, 'p2',  '2015-01-08 09:25:35', 50),
    (1, 'p3',  '2015-01-08 09:26:25', 48),
    (1, 'p4',  '2015-01-08 09:27:23', 36),
    (1, 'p5',  '2015-01-08 09:27:59', 41),
    (1, 'p6',  '2015-01-08 09:28:40', 70),
    (1, 'p7',  '2015-01-08 09:29:50', 50),
    (1, 'p8',  '2015-01-08 09:30:40', 45),
    (1, 'p9',  '2015-01-08 09:31:25', 35),
    (1, 'p10', '2015-01-08 09:32:00', null),
    (2, 'pll', '2015-01-08 09:25:35', 25),
    (2, 'p12', '2015-01-08 09:26:00', 55),
    (2, 'p13', '2015-01-08 09:26:55', 30),
    (2, 'p14', '2015-01-08 09:27:25', 95),
    (2, 'p15', '2015-01-08 09:29:00', null),
    (3, 'p16', '2015-01-08 10:41:00', 65),
    (3, 'p17', '2015-01-08 10:42:05', 75),
    (3, 'p18', '2015-01-08 10:43:20', 90),
    (3, 'p19', '2015-01-08 10:43:20', 39),
    (3, 'p20', '2015-01-08 10:43:59', 50),
    (3, 'p21', '2015-01-08 10:44:49', null);
21 rows affected

explain (analyze,buffers)
with A as (
    select seller_id, payment_time, second_diff,
        case when
            lag(case when second_diff < 60 then 1 else 0 end)
                over (partition by seller_id order by payment_time)
              = case when second_diff < 60 then 1 else 0 end
            then 0 else 1 end as transition
    from T
), B as (
    select *,
        sum(transition)
            over (partition by seller_id order by payment_time) as grp
    from A
), C as (
    select seller_id, count(*) as p
    from B
    where second_diff < 60
    group by seller_id, grp
    having count(*) >= 3
) 
select count(distinct seller_id) as sellers, sum(p) as payments
from C;


QUERY PLAN


Aggregate  (cost=298.65..298.66 rows=1 width=40) (actual time=3.524..3.525 rows=1 loops=1)

  Buffers: shared hit=7

  CTE a

    ->  WindowAgg  (cost=94.38..131.78 rows=1360 width=20) (actual time=0.087..0.137 rows=21 loops=1)

          Buffers: shared hit=1

          ->  Sort  (cost=94.38..97.78 rows=1360 width=16) (actual time=0.054..0.071 rows=21 loops=1)

                Sort Key: t.seller_id, t.payment_time

                Sort Method: quicksort  Memory: 26kB

                Buffers: shared hit=1

                ->  Seq Scan on t  (cost=0.00..23.60 rows=1360 width=16) (actual time=0.015..0.021 rows=21 loops=1)

                      Buffers: shared hit=1

  CTE b

    ->  WindowAgg  (cost=97.98..125.18 rows=1360 width=28) (actual time=0.219..0.237 rows=21 loops=1)

          Buffers: shared hit=7

          ->  Sort  (cost=97.98..101.38 rows=1360 width=20) (actual time=0.204..0.205 rows=21 loops=1)

                Sort Key: a.seller_id, a.payment_time

                Sort Method: quicksort  Memory: 26kB

                Buffers: shared hit=7

                ->  CTE Scan on a  (cost=0.00..27.20 rows=1360 width=20) (actual time=0.088..0.145 rows=21 loops=1)

                      Buffers: shared hit=1

  CTE c

    ->  HashAggregate  (cost=35.13..37.00 rows=187 width=20) (actual time=0.271..0.274 rows=3 loops=1)

          Group Key: b.seller_id, b.grp

          Filter: (count(*) >= 3)

          Rows Removed by Filter: 1

          Buffers: shared hit=7

          ->  CTE Scan on b  (cost=0.00..30.60 rows=453 width=12) (actual time=0.232..0.252 rows=12 loops=1)

                Filter: (second_diff < 60)

                Rows Removed by Filter: 9

                Buffers: shared hit=7

  ->  CTE Scan on c  (cost=0.00..3.74 rows=187 width=12) (actual time=0.274..0.281 rows=3 loops=1)

        Buffers: shared hit=7

Planning time: 2.486 ms

Execution time: 7.750 ms


explain (analyze,buffers)
with A as (
    select seller_id, payment_time, second_diff,
        case when
            lag(case when second_diff < 60 then 1 else 0 end)
                over (partition by seller_id order by payment_time)
              = case when second_diff < 60 then 1 else 0 end
            then 0 else 1 end as transition
    from T
), B as (
    select *,
        sum(transition)
            over (partition by seller_id order by payment_time) as grp
    from A
)
select
    dense_rank() over (order by seller_id)
      + dense_rank() over (order by seller_id desc) - 1 as sellers,
    sum(count(*)) over () as payments
from B
where second_diff < 60
group by seller_id, grp
having count(*) >= 3
limit 1;


QUERY PLAN


Limit  (cost=311.35..311.39 rows=1 width=52) (actual time=0.272..0.272 rows=1 loops=1)

  Buffers: shared hit=1

  CTE a

    ->  WindowAgg  (cost=94.38..131.78 rows=1360 width=20) (actual time=0.065..0.086 rows=21 loops=1)

          Buffers: shared hit=1

          ->  Sort  (cost=94.38..97.78 rows=1360 width=16) (actual time=0.049..0.050 rows=21 loops=1)

                Sort Key: t.seller_id, t.payment_time

                Sort Method: quicksort  Memory: 26kB

                Buffers: shared hit=1

                ->  Seq Scan on t  (cost=0.00..23.60 rows=1360 width=16) (actual time=0.011..0.014 rows=21 loops=1)

                      Buffers: shared hit=1

  CTE b

    ->  WindowAgg  (cost=97.98..125.18 rows=1360 width=28) (actual time=0.141..0.157 rows=21 loops=1)

          Buffers: shared hit=1

          ->  Sort  (cost=97.98..101.38 rows=1360 width=20) (actual time=0.131..0.132 rows=21 loops=1)

                Sort Key: a.seller_id, a.payment_time

                Sort Method: quicksort  Memory: 26kB

                Buffers: shared hit=1

                ->  CTE Scan on a  (cost=0.00..27.20 rows=1360 width=20) (actual time=0.066..0.091 rows=21 loops=1)

                      Buffers: shared hit=1

  ->  WindowAgg  (cost=54.39..60.93 rows=187 width=52) (actual time=0.265..0.265 rows=1 loops=1)

        Buffers: shared hit=1

        ->  WindowAgg  (cost=54.39..57.66 rows=187 width=36) (actual time=0.244..0.246 rows=3 loops=1)

              Buffers: shared hit=1

              ->  Sort  (cost=54.39..54.85 rows=187 width=28) (actual time=0.240..0.241 rows=3 loops=1)

                    Sort Key: b.seller_id DESC

                    Sort Method: quicksort  Memory: 25kB

                    Buffers: shared hit=1

                    ->  WindowAgg  (cost=44.06..47.33 rows=187 width=28) (actual time=0.217..0.221 rows=3 loops=1)

                          Buffers: shared hit=1

                          ->  Sort  (cost=44.06..44.52 rows=187 width=20) (actual time=0.208..0.208 rows=3 loops=1)

                                Sort Key: b.seller_id

                                Sort Method: quicksort  Memory: 25kB

                                Buffers: shared hit=1

                                ->  HashAggregate  (cost=35.13..37.00 rows=187 width=20) (actual time=0.196..0.198 rows=3 loops=1)

                                      Group Key: b.seller_id, b.grp

                                      Filter: (count(*) >= 3)

                                      Rows Removed by Filter: 1

                                      Buffers: shared hit=1

                                      ->  CTE Scan on b  (cost=0.00..30.60 rows=453 width=12) (actual time=0.153..0.177 rows=12 loops=1)

                                            Filter: (second_diff < 60)

                                            Rows Removed by Filter: 9

                                            Buffers: shared hit=1

Planning time: 0.545 ms

Execution time: 0.401 ms


explain (analyze,buffers)
with A as (
    select seller_id, payment_time, second_diff,
        row_number() over (partition by seller_id order by payment_time) as rn
    from T
), B as (
    select *,
        rn - row_number() over (partition by seller_id order by payment_time) as grp
    from A
    where second_diff < 60    
), C as (
    select seller_id, count(*) as p
    from B
    group by seller_id, grp
    having count(*) >= 3
) 
select count(distinct seller_id) as sellers, sum(p) as payments
from C;


QUERY PLAN


Aggregate  (cost=202.95..202.96 rows=1 width=40) (actual time=0.142..0.142 rows=1 loops=1)

  Buffers: shared hit=1

  CTE a

    ->  WindowAgg  (cost=94.38..121.58 rows=1360 width=24) (actual time=0.038..0.054 rows=21 loops=1)

          Buffers: shared hit=1

          ->  Sort  (cost=94.38..97.78 rows=1360 width=16) (actual time=0.031..0.033 rows=21 loops=1)

                Sort Key: t.seller_id, t.payment_time

                Sort Method: quicksort  Memory: 26kB

                Buffers: shared hit=1

                ->  Seq Scan on t  (cost=0.00..23.60 rows=1360 width=16) (actual time=0.008..0.010 rows=21 loops=1)

                      Buffers: shared hit=1

  CTE b

    ->  WindowAgg  (cost=50.58..60.78 rows=453 width=32) (actual time=0.089..0.095 rows=12 loops=1)

          Buffers: shared hit=1

          ->  Sort  (cost=50.58..51.72 rows=453 width=24) (actual time=0.082..0.082 rows=12 loops=1)

                Sort Key: a.seller_id, a.payment_time

                Sort Method: quicksort  Memory: 25kB

                Buffers: shared hit=1

                ->  CTE Scan on a  (cost=0.00..30.60 rows=453 width=24) (actual time=0.048..0.066 rows=12 loops=1)

                      Filter: (second_diff < 60)

                      Rows Removed by Filter: 9

                      Buffers: shared hit=1

  CTE c

    ->  HashAggregate  (cost=13.59..15.59 rows=200 width=20) (actual time=0.114..0.115 rows=3 loops=1)

          Group Key: b.seller_id, b.grp

          Filter: (count(*) >= 3)

          Rows Removed by Filter: 1

          Buffers: shared hit=1

          ->  CTE Scan on b  (cost=0.00..9.06 rows=453 width=12) (actual time=0.089..0.096 rows=12 loops=1)

                Buffers: shared hit=1

  ->  CTE Scan on c  (cost=0.00..4.00 rows=200 width=12) (actual time=0.115..0.119 rows=3 loops=1)

        Buffers: shared hit=1

Planning time: 0.101 ms

Execution time: 0.231 ms