1

時間間隔と天気の説明によっていくつかの天気データをグループ化する with 句があります。

With 
temp_table (counter, hour, current_Weather_description) as
(
    SELECT count(*) as counter,
           CASE WHEN  strftime('%M',  time_stamp) < '30' 
                THEN cast(strftime('%H', time_stamp)  as int)
                ELSE cast(strftime('%H', time_stamp, '+1 hours') as int)
           END as hour,
           current_weather_description
    FROM weather_events
    GROUP BY strftime('%H',  time_stamp, '+30 minutes'),
             current_Weather_Description
    order by hour desc 
)
select *
from temp_table

結果 {counter, hour, current_weather_description}:

"1" "10" "Cloudy"

"2" "9" "Clear"
"1" "9" "Meatballs"

"2" "8" "Rain"

"2" "7" "Clear"

"2" "6" "Clear"

"1" "5" "Clear"
"1" "5" "Cloudy"

"1" "4" "Clear"
"1" "4" "Rain"

"1" "3" "Rain"
"1" "3" "Snow"

"1" "2" "Rain"

ここで、1 時間ごとに一番上の行を選択する再帰クエリを作成したいと思います。一番上の行には、その時間間隔で発生 (カウント) が最も多い説明が常に含まれます。同数の場合でも、一番上の行が選択されます。これが私の最初の試みです：

With recursive
temp_table (counter, hour, current_Weather_description) as
(
    SELECT count(*) as counter,
           CASE WHEN  strftime('%M',  time_stamp) < '30' 
                THEN cast(strftime('%H', time_stamp)  as int)
                ELSE cast(strftime('%H', time_stamp, '+1 hours') as int)
           END as hour,
           current_weather_description
    FROM weather_events
    GROUP BY strftime('%H',  time_stamp, '+30 minutes'),
             current_Weather_Description
    order by hour desc 
),
segment (anchor_hour, hour, current_Weather_description) as
(
    select cast(strftime('%H','2016-01-20 10:14:17') as int) as anchor_hour,
           hour,
           current_Weather_Description
    from temp_table
    where hour = anchor_hour
    limit 1
    union all
    select segment.anchor_hour-1,
           hour,
           current_Weather_Description
    from temp_table
    where hour = anchor_hour - 1
    limit 1
)
select *
from segment

クエリをいじってみると、temp_table ではなく "segment" からの再帰メンバーを "from" にしたいようです。なぜそれが私にそれをさせたいのか理解できません。この例と似たようなことをしようとしていますが、各再帰クエリから 1 行だけが必要です。

これは私が望む結果です{カウント、時間、説明}:

    "1" "10" "Cloudy"

    "2" "9" "Clear"

    "2" "8" "Rain"

    "2" "7" "Clear"

    "2" "6" "Clear"

    "1" "5" "Clear"

    "1" "4" "Clear"

    "1" "3" "Rain"

    "1" "2" "Rain"
4

1 に答える 1

1

これは、別の GROUP BY を使用して簡単に実行できます。

WITH
temp_table(counter, hour, current_Weather_description) AS (
    ...
),
segment(count, hour, description) AS (
    SELECT MAX(counter),
           hour,
           current_Weather_description
    FROM temp_table
    GROUP BY hour
)
SELECT count, hour, description
FROM segment
ORDER BY hour DESC;

(SQLite では、MAX() を使用して、グループから行全体を選択できます。)

于 2016-01-21T08:06:57.150 に答える