のPostgres：彼らは私がPostgresの9.2を実行している

Question

を発生し、温度およびタイムスタンプ、ミリ秒エポック時間で毎分1つのタイムスタンプのテーブル持っている最大値と最小値を取得し、タイムスタンプ：私が持っている

weather=# \d weather_data 
     Table "public.weather_data" 
    Column |  Type  | Modifiers 
-------------+--------------+----------- 
timestamp | bigint  | not null 
sensor_id | integer  | not null 
temperature | numeric(4,1) | 
humidity | integer  | 
date  | date   | not null 
Indexes: 
    "weather_data_pkey" PRIMARY KEY, btree ("timestamp", sensor_id) 
    "weather_data_date_idx" btree (date) 
    "weather_data_humidity_idx" btree (humidity) 
    "weather_data_sensor_id_idx" btree (sensor_id) 
    "weather_data_temperature_idx" btree (temperature) 
    "weather_data_time_idx" btree ("timestamp") 
Foreign-key constraints: 
    "weather_data_sensor_id_fkey" FOREIGN KEY (sensor_id) REFERENCES weather_sensors(sensor_id) 

weather=# select * from weather_data order by timestamp desc; 
    timestamp | sensor_id | temperature | humidity | date  
---------------+-----------+-------------+----------+------------ 
1483272420000 |   2 |  22.3 |  57 | 2017-01-01 
1483272420000 |   1 |  24.9 |  53 | 2017-01-01 
1483272360000 |   2 |  22.3 |  57 | 2017-01-01 
1483272360000 |   1 |  24.9 |  58 | 2017-01-01 
1483272300000 |   2 |  22.4 |  57 | 2017-01-01 
1483272300000 |   1 |  24.9 |  57 | 2017-01-01 
[...] 

をこの既存の毎日の高値と安値を取得するクエリが、その高いか低いが発生したことをない特定の時間：

WITH t AS (
    SELECT date, highest, lowest 
    FROM (
     SELECT date, max(temperature) AS highest 
     FROM weather_data 
     WHERE sensor_id = (SELECT sensor_id FROM weather_sensors WHERE sensor_name = 'outdoor') 
     GROUP BY date 
     ORDER BY date ASC 
    ) h 
    INNER JOIN (
     SELECT date, min(temperature) AS lowest 
     FROM weather_data 
     WHERE sensor_id = (SELECT sensor_id FROM weather_sensors WHERE sensor_name = 'outdoor') 
     GROUP BY date 
     ORDER BY date ASC 
    ) l 
    USING (date) 
    ORDER BY date DESC 
) 
SELECT * from t ORDER BY date ASC; 

の2つのがあり万行を超えるビットは、データベース内だと、それは〜1.2秒かかります実行する 残念な。私は今、高いか低いがあったことを特定の時刻を取得したい、私はが作業を行い、この使用してウィンドウ関数、思い付いたけど〜5.6秒かかる：

SELECT h.date, high_time, high_temp, low_time, low_temp FROM (
    SELECT date, high_temp, high_time FROM (
     SELECT date, temperature AS high_temp, timestamp AS high_time, row_number() 
     OVER (PARTITION BY date ORDER BY temperature DESC, timestamp DESC) 
     FROM weather_data 
     WHERE sensor_id = (SELECT sensor_id FROM weather_sensors WHERE sensor_name = 'outdoor') 
    ) highs 
    WHERE row_number = 1 
) h 
INNER JOIN (
    SELECT * FROM (
     SELECT date, temperature AS low_temp, timestamp AS low_time, row_number() 
     OVER (PARTITION BY date ORDER BY temperature ASC, timestamp DESC) 
     FROM weather_data 
     WHERE sensor_id = (SELECT sensor_id FROM weather_sensors WHERE sensor_name = 'outdoor') 
    ) lows 
    WHERE row_number = 1 
) l 
ON h.date = l.date 
ORDER BY h.date ASC; 

をするいくつかの比較的単純な加算があります私はそれが実行時間の大量を追加しません作ることができる最初のクエリ？私はそこにあると仮定しますが、私は私が問題をあまりにも長く見ていた時点にいると思います！

Answer 1

SELECT 
     DISTINCT ON (zdate) zdate 
     , first_value(ztimestamp) OVER www AS stamp_at_min 
     , first_value(temperature) OVER www AS tmin 
     , last_value(ztimestamp) OVER www AS stamp_at_max 
     , last_value(temperature) OVER www AS tmax 
FROM weather_data 
WHERE sensor_id = 2 
WINDOW www AS (PARTITION BY zdate ORDER BY temperature, ztimestamp 
       ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING 
       ) 
     ; 

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• Iは、[のPostgreSQL

Answer 2

これはあなたの2番目のクエリと同じことが、唯一のweather_dataテーブル上の単一のスキャン必要があります：それは結果に（別名「ピボット」）クエリクロス集計を行うには、条件付き集約を使用しています

select date, 
     max(case when high_rn = 1 then timestamp end) as high_time, 
     max(case when high_rn = 1 then temperature end) as high_temp, 
     max(case when low_rn = 1 then timestamp end) as low_time, 
     max(case when low_rn = 1 then temperature end) as low_temp 
from (
    select timestamp, temperature, date, 
     row_number() OVER (PARTITION BY date ORDER BY temperature DESC, timestamp DESC) as high_rn, 
     row_number() OVER (PARTITION BY date ORDER BY temperature ASC, timestamp DESC) as low_rn 
    from weather_data 
    where sensor_id = ... 
) t 
where (high_rn = 1 or low_rn = 1) 
group by date; 

をその最低温度と最高温度のみが含まれています。

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^{関連のない、しかし：dateとtimestampは列のために恐ろしい名前です。 1つはキーワードなので、もっと重要なのは列の実際の意味を文書化していないからです。それは「期日」ですか？ 「読書日」？ 「処理日」？}