將同一個表連接兩次而不存在重複行

Question

問題：兩次連接同一個表後，我得到很多重複的行和很長的查詢。

有兩個表：

活動：事項標識，EVENT_TIME，EVENT_NAME TSERIES：data_time，數據

的EVENT_TIME是爲特定事件時，data_time在每分鐘有數據。

我要輸出一個表，其中我將有6列： EVENT_ID，EVENT_TIME，data_time1，DATA1，data_time2，DATA2 其中data_time1/DATA1是用於第2分鐘的情況下（0後，1 ）， 和data_time2/data2的下一個2分鐘（3，4）

我的查詢：

SELECT 
* 
FROM events 
LEFT JOIN tseries ts1 
ON ts1.data_time >= (events.event_time) AND ts1.data_time <= (events.event_time + time '00:01:00') 
LEFT JOIN tseries ts2 
ON ts2.data_time >= (events.event_time + time '00:02:00') AND ts2.data_time <= (events.event_time + time '00:03:00') 
ORDER BY events.event_id 
; 

該查詢生成該表（I僅包括時間數據），以及接合後同一張表更多次會更可怕。

event_time data_time1 data_time2 
    x  x+0  x+2 
    x  x+0  x+3 
    x  x+1  x+2 
    x  x+1  x+3 

我寧願這樣的事情，而不是：

event_time data_time1 data_time2 
    x  x+0  x+2 
    x  x+1  x+3 

或

event_time data_time1 data_time2 
    x  x+0  null 
    x  x+1  null 
    x  null  x+2 
    x  null  x+3 

任何想法？感謝您的幫助/答案:)

Answer 1

一種方法是有條件的聚集。 。 。假設每個事件只需要一行：

SELECT e.*, 
     MAX(CASE WHEN ts.data_time >= e.event_time AND ts1.data_time <= e.event_time + time '00:01:00' THEN ts.data END) as data_1, 
     MAX(CASE WHEN ts.data_time >= e.event_time + time '00:02:00' AND ts2.data_time <= e.event_time + time '00:03:00' THEN ts.data END) as data_2 
FROM events e LEFT JOIN 
    tseries ts 
    ON (ts.data_time >= e.event_time AND ts1.data_time <= e.event_time + time '00:01:00') OR 
     (ts.data_time >= e.event_time + time '00:02:00' AND ts2.data_time <= e.event_time + time '00:03:00') 
GROUP BY e.event_id 
ORDER BY e.event_id; 

但是，這不適用於每個時間段內的多個匹配項。

對於多行，一種方法是枚舉每個事件和每個時間段的值。然後，您可以使用該序號進行匹配。下面使用的情況下，FULL JOIN兩個列表中有不同的長度：

SELECT COALESCE(ts1.event_id, ts2.event_id) as event_id, 
     ts1.data, ts2.data 
FROM (SELECT e.event_id, ts1.data, 
      ROW_NUMBER() OVER (PARTITION BY e.event_id ORDER BY ts1.event_time) as seqnum 
     FROM events e JOIN 
      tseries ts1 
      ON ts1.data_time >= e.event_time AND 
       ts1.data_time <= e.event_time + time '00:01:00' 
    ) ts1 FULL JOIN 
    (SELECT e.event_id, ts1.data, 
      ROW_NUMBER() OVER (PARTITION BY e.event_id ORDER BY ts1.event_time) as seqnum 
     FROM events e JOIN 
      tseries ts2 
      ON ts1.data_time >= e.event_time + time '00:02:00' AND 
       ts1.data_time <= e.event_time + time '00:03:00' 
    ) ts2 
    ON ts1.event_id = ts2.event_id AND ts1.seqnum = ts2.seqnum 
ORDER BY event_id; 

注意：如果你想從event其他字段，那麼你可以使用：

SELECT e.*, 
     ts1.data, ts2.data 
FROM events e LEFT JOIN 
    (SELECT e.event_id, ts1.data, 
      ROW_NUMBER() OVER (PARTITION BY e.event_id ORDER BY ts1.event_time) as seqnum 
     FROM events e JOIN 
      tseries ts1 
      ON ts1.data_time >= e.event_time AND 
       ts1.data_time <= e.event_time + time '00:01:00' 
    ) ts1 
    ON ts1.event_id = e.event_id LEFT JOIN 
    (SELECT e.event_id, ts1.data, 
      ROW_NUMBER() OVER (PARTITION BY e.event_id ORDER BY ts1.event_time) as seqnum 
     FROM events e JOIN 
      tseries ts2 
      ON ts1.data_time >= e.event_time + time '00:02:00' AND 
       ts1.data_time <= e.event_time + time '00:03:00' 
    ) ts2 
    ON e.event_id = ts2.event_id AND ts1.seqnum = ts2.seqnum 
ORDER BY e.event_id; 

Answer 2

嘗試

SELECT distinct 
* 
FROM events 
LEFT JOIN tseries ts1 
ON ts1.data_time >= (events.event_time) AND ts1.data_time <= (events.event_time + time '00:01:00') 
LEFT JOIN tseries ts2 
ON ts2.data_time >= (events.event_time + time '00:02:00') AND ts2.data_time <= (events.event_time + time '00:03:00') 
ORDER BY events.event_id;