Finding the longest streak of wins

Question

I have data in following format.

match_id   team_id   won_ind
----------------------------
37          Team1    N
67          Team1    Y
98          Team1    N
109         Team1    N
158         Team1    Y
162         Team1    Y
177         Team1    Y
188         Team1    Y
198         Team1    N
207         Team1    Y
217         Team1    Y
10          Team2    N
13          Team2    N
24          Team2    N
39          Team2    Y
40          Team2    Y
51          Team2    Y
64          Team2    N
79          Team2    N
86          Team2    N
91          Team2    Y
101         Team2    N

Here match_ids are in chronological order, 37 is the first and 217 is the last match played by team1. won_ind indicated whether the team won the match or not.

So, from the above data, team1 has lost its first match, then won a match, then lost 2 matches, then won 4 consecutive matches and so on. Now I'm interested in finding the longest winning streak for each team.

Team_id   longest_streak
------------------------
Team1     4
Team2     3

I know how to find this in plsql, but i was wondering if this can be calculated in pure SQL. I tried using LEAD, LAG and several other functions, but not getting anywhere.

I have created sample fiddle here.

Answer 1

with original_data as (
  select 37  match_id, 'Team1' team_id, 'N' won_id from dual union all
  select 67  match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 98  match_id, 'Team1' team_id, 'N' won_id from dual union all
  select 109 match_id, 'Team1' team_id, 'N' won_id from dual union all
  select 158 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 162 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 177 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 188 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 198 match_id, 'Team1' team_id, 'N' won_id from dual union all
  select 207 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 217 match_id, 'Team1' team_id, 'Y' won_id from dual union all
  select 10  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 13  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 24  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 39  match_id, 'Team2' team_id, 'Y' won_id from dual union all
  select 40  match_id, 'Team2' team_id, 'Y' won_id from dual union all
  select 51  match_id, 'Team2' team_id, 'Y' won_id from dual union all
  select 64  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 79  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 86  match_id, 'Team2' team_id, 'N' won_id from dual union all
  select 91  match_id, 'Team2' team_id, 'Y' won_id from dual union all
  select 101 match_id, 'Team2' team_id, 'N' won_id from dual 
),
----------------------------------------------------------------------
new_streaks as (
--
--  Identifying new streaks.
--  ------------------------
--
    select
      match_id,
      team_id,
      won_id,
--
--  A new streak is identfied if 
--
    case when
--
--    a) won_id = 'Y' and
--
      won_id = 'Y' and
--
--    b) the previous won_id = 'N':
--    
      lag(won_id) over (partition by team_id order by match_id) = 'N' 
--
--    
      then 1 
--
--    All other cases: no new streak:
      else 0 
-- 
     end new_streak
    from
      original_data
),
-------------------------------
streak_no as (
--
--  Assigning a unique number to each streak.
--  -----------------------------------------
--
select
--
    match_id,
    team_id,
--
--  In order to be able to count the number of records
--  of a streak, we first need to assign a unique number
--  to each streak:
--
    sum(new_streak) over (partition by team_id order by match_id) streak_no
--
from
    new_streaks 
where
--  We're only interested in «winning streaks»:
    won_id = 'Y'
),
-----------------------------------------------
--
--  Counting the elements per streak
--  --------------------------------
--
records_per_streak as (
select 
  count(*) counter,
  team_id,
  streak_no
from
  streak_no
group by
  team_id,
  streak_no
)
------------------------------------------------
--
--   Finally: we can find the «longest streak»
--   per team:
--
select
  max(counter) longest_streak,
  team_id
from
  records_per_streak 
group by team_id
;

Answer 2

I had a similar task on Teradata, modified it to run on Oracle:

SELECT
   team_id,
   MAX(cnt)
FROM
 (
   SELECT
      team_id,
      COUNT(*) AS cnt
   FROM 
    (
      SELECT
        team_id, 
        match_id,
        won_ind,
        SUM(CASE WHEN won_ind <> 'Y' THEN 1 END) 
        OVER (PARTITION BY team_id 
              ORDER BY match_id 
              ROWS UNBOUNDED PRECEDING) AS dummy
      FROM matches
    ) dt
   WHERE won_ind = 'Y'
   GROUP BY team_id, dummy
 ) dt
GROUP BY team_id;