PostgreSQLの - 最新かつ特定のレコードの取得数

Question

私はテーブルを持っている：すべてのsidは、指定されたtimestampでいくつかのtypeとstatusに到達したときに記録

select sid, type, status, timestamp from contact_history limit 10; 
      sid | type | status |   timestamp 
     ---------+------+--------+------------------------------- 
     6291179 | 0 | 1025 | 2015-08-24 13:05:22.501025+02 
     68737 | 0 |  5 | 2015-08-24 13:05:32.500005+02 
     4987391 | 0 |  65 | 2015-08-24 13:05:35.500065+02 
     1189551 | 1 |  65 | 2015-08-24 13:06:05.510065+02 
     3374714 | 1 |  5 | 2015-07-27 13:25:25.510005+02 
     2297221 | 0 |  5 | 2015-07-27 13:25:48.500005+02 
     5503230 | 2 |  65 | 2015-07-27 13:25:50.520065+02 
     596992 | 1 |  65 | 2015-07-27 13:26:51.510065+02 
     5215455 | 0 | 1025 | 2015-07-27 13:27:21.501025+02 
     3011248 | 0 |  5 | 2015-07-27 13:27:46.500005+02 
     (10 rows) 


\d contact_history 
             Table "contact_history" 
     Column  |   Type   |       Modifiers 
    ---------------+--------------------------+---------------------------------------------------------- 
    sid   | character varying(32) | not null 
    type   | integer     | not null 
    status  | integer     | not null 
    timestamp  | timestamp with time zone | not null 
    id   | bigint     | not null default nextval('contact_history_id_seq'::regcla 
    Indexes: 
     "contact_history_pk" PRIMARY KEY, btree (id) 
     "contact_history_sid_timestamp_idx" btree (sid, "timestamp") 

。一意の行はありません。 sidはいつでもランダムにtypeとstatusをランダムに並べ替えることができます。 20万の行があります。 PostgreSQLのバージョンは9.3.13です

今度はsidがどれくらいあるか知りたいのですが、に今すぐ - >max(timestamp)があります。言い換えれば、sidの場合は、最後にtimestampと対応するtypeとstatusを見つけて、条件が(type='0' or type='1') and status='5'であるものを数えます。だから私は出力として1つの数字を期待しています。他のより効率的なアプローチと同じ結果を歓迎します。ありがとうございました。

Answer 1

a_horse_with_no_nameのおかげで、グループごとの最大のパスに従います。残念ながらそれは少し異なります。私はいくつかの猿の設計を行なったし、これまでのところ、私は別のコストと、次のクエリました：

EXPLAIN SELECT count(*) FROM contact_history t1 LEFT OUTER JOIN contact_history t2 ON (t1.sid = t2.sid AND t1.timestamp < t2.timestamp) WHERE t2.sid IS NULL and (t1.type=0 OR t1.type=1) and t1.status = '5'; 
              QUERY PLAN 
----------------------------------------------------------------------------------------------- 
Aggregate (cost=158816.96..158816.97 rows=1 width=0) 
    -> Hash Anti Join (cost=66228.91..158003.37 rows=325435 width=0) 
     Hash Cond: ((t1.sid)::text = (t2.sid)::text) 
     Join Filter: (t1."timestamp" < t2."timestamp") 
     -> Seq Scan on contact_history t1 (cost=0.00..50771.93 rows=488152 width=15) 
       Filter: ((status = 5) AND ((type = 0) OR (type = 1))) 
     -> Hash (cost=39041.96..39041.96 rows=1563996 width=15) 
       -> Seq Scan on contact_history t2 (cost=0.00..39041.96 rows=1563996 width=15) 
(8 rows) 

EXPLAIN SELECT count(*) from contact_history as ch, (select sid, max(timestamp) as max_t from contact_history group by sid) as sub where ch.sid=sub.sid and ch.timestamp=sub.max_t and (type='0' or type='1') and status = '5'; 
              QUERY PLAN 
---------------------------------------------------------------------------------------------------- 
Aggregate (cost=393277.11..393277.12 rows=1 width=0) 
    -> Merge Join (cost=366994.07..393277.10 rows=2 width=0) 
     Merge Cond: ((contact_history.sid)::text = (ch.sid)::text) 
     Join Filter: (ch."timestamp" = (max(contact_history."timestamp"))) 
     -> GroupAggregate (cost=253411.17..267270.04 rows=212890 width=15) 
       -> Sort (cost=253411.17..257321.16 rows=1563996 width=15) 
        Sort Key: contact_history.sid 
        -> Seq Scan on contact_history (cost=0.00..39041.96 rows=1563996 width=15) 
     -> Materialize (cost=113582.90..116023.66 rows=488152 width=15) 
       -> Sort (cost=113582.90..114803.28 rows=488152 width=15) 
        Sort Key: ch.sid 
        -> Seq Scan on contact_history ch (cost=0.00..50771.93 rows=488152 width=15) 
          Filter: ((status = 5) AND ((type = 0) OR (type = 1))) 
(13 rows) 

EXPLAIN SELECT count(*) FROM contact_history as ch1 WHERE timestamp = (SELECT MAX(timestamp) FROM contact_history AS ch2 WHERE ch1.sid = ch2.sid) and (ch1.type='0' or ch1.type='1') and ch1.status = '5'; 
                     QUERY PLAN 

----------------------------------------------------------------------------------------------------- 
--------------------------------------------------- 
Aggregate (cost=7919844.02..7919844.03 rows=1 width=0) 
    -> Seq Scan on contact_history ch1 (cost=0.00..7919837.92 rows=2441 width=0) 
     Filter: ((status = 5) AND ((type = 0) OR (type = 1)) AND ("timestamp" = (SubPlan 2))) 
     SubPlan 2 
      -> Result (cost=5.02..5.03 rows=1 width=0) 
       InitPlan 1 (returns $1) 
        -> Limit (cost=0.43..5.02 rows=1 width=8) 
         -> Index Only Scan Backward using contact_history_sid_timestamp_idx on cont 
act_history ch2 (cost=0.43..32.57 rows=7 width=8) 
           Index Cond: ((sid = (ch1.sid)::text) AND ("timestamp" IS NOT NULL)) 
(9 rows) 

いくつかの改善、さらに、コメントや歓迎以上の説明を。ありがとうございました。