SQL/Teradata：如何返回特定值及其前面的行？

Question

我有一個SQL（Teradata）問題，我一直無法解決。我知道答案可能比我看起來更簡單。

我有這樣一組代碼：

ID  timestamp   location  event_type 
1111 20160601-0112  Detroit  Event A 
1111 20160602-0954  Brooklyn  Event B 
1111 20160602-1123  Brooklyn  Event A 
1112 20160912-1420  Minneapolis Event B 
1113 20161123-1742  New Orleans Event A 
1113 20161124-1841  New Orleans Event A 
1113 20161124-2100  New Orleans Event B 
1114 20170201-0959  Detroit  Event A 
1114 20170201-2350  Detroit  Event A 

這裏是條件什麼，我需要返回：

我想回到每個ID的第一個事件B，和最近的事件在事件B之前發生的事件（基於時間戳）。因此，對於上面的數據集，我會得到：

ID  timestamp   location  event_type 
1111 20160601-0112  Detroit  Event A 
1111 20160602-0954  Brooklyn  Event B 
1113 20161124-1841  New Orleans Event A 
1113 20161124-2100  New Orleans Event B 

爲1111第三個記錄沒有得到恢復，因爲它發生後，事件B. ID 1112沒有得到恢復，因爲它不具有事件A在它之前。 1113的第一條記錄不會被返回，因爲在它之後有更接近的事件A（到事件B）。 1114沒有得到返回，因爲沒有事件B.

我一直在這個工作了幾個小時到了我不再接近它的地步......任何幫助將不勝感激！

Answer 1

這與MS SQL 2012的工作 - 不知道如果語法是相同的？

;WITH myData AS 
    (
     SELECT 
      ID, 
      min(timestamp) as timestamp, 
      location, 
      event_type 
     FROM 
      tableName 
     GROUP BY 
      ID, 
      location, 
      event_type 
    ) 
     SELECT 
      * 
     FROM 
      myData 
     WHERE 
      (
       myData.timestamp < (SELECT top 1 m2.timestamp FROM myData m2 WHERE m2.ID = myData.ID AND m2.event_type = 'Event B' ORDER BY m2.timestamp ASC) 
       OR 
       myData.event_type = 'Event B' 
      ) 
      AND (SELECT Count(*) FROM myData m2 WHERE m2.ID = myData.ID AND m2.event_type = 'Event A') > 0 
     ORDER BY 
      myData.timestamp 

Answer 2

鑑於您的示例數據，我認爲以下幾點應該可以做到。

SELECT * 
FROM testtable 
QUALIFY 

    (
     event_type = 'Event A' 
     AND 
     min(event_type) OVER (PARTITION BY id ORDER BY "timestamp" ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) = 'Event B' 
    ) OR 
    (
     event_type = 'Event B' 
     AND 
     max(event_type) OVER (PARTITION BY id ORDER BY "timestamp" ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) = 'Event A' 
    ) 

這裏我們使用Window函數來測試結果集中記錄之前和之後的記錄。我們在QUALIFY子句中這樣做，就像WHERE子句一樣，但是對於窗口函數。

打破這個資格聲明：

 event_type = 'Event A' 
     AND 
     min(event_type) OVER (PARTITION BY id ORDER BY "timestamp" ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) = 'Event B' 

是說：「如果這個當前記錄是‘事件A’，當按時間戳此ID下令第二天記錄‘事件B’則允許記錄」。

 event_type = 'Event B' 
     AND 
     max(event_type) OVER (PARTITION BY id ORDER BY "timestamp" ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) = 'Event A' 

是說：「如果這個當前記錄‘事件B’，當按時間戳此ID訂購了此前的紀錄是‘事件A’則允許記錄。

可能需要得到在更多的創造QUALIFY條款搭上邊的情況，但一旦你換你的頭周圍一切是如何運作的，你可以在那裏得到相當的創意

---

例：

CREATE MULTISET VOLATILE TABLE testtable 
(
id int, 
ts varchar(20), 
location varchar(20), 
event_type varchar(20) 

) PRIMARY INDEX (id) ON COMMIT PRESERVE ROWS; 

INSERT INTO testtable VALUES (1111,'20160601-0112','Detroit','Event A'); 
INSERT INTO testtable VALUES (1111,'20160602-0954','Brooklyn','Event B'); 
INSERT INTO testtable VALUES (1111,'20160602-1123','Brooklyn','Event A'); 
INSERT INTO testtable VALUES (1112,'20160912-1420','Minneapolis','Event B'); 
INSERT INTO testtable VALUES (1113,'20161123-1742','New Orleans','Event A'); 
INSERT INTO testtable VALUES (1113,'20161124-1841','New Orleans','Event A'); 
INSERT INTO testtable VALUES (1113,'20161124-2100','New Orleans','Event B'); 
INSERT INTO testtable VALUES (1114,'20170201-0959','Detroit','Event A'); 
INSERT INTO testtable VALUES (1114,'20170201-2350','Detroit','Event A'); 


SELECT * 
FROM testtable 
QUALIFY 

    (
     event_type = 'Event A' 
     AND 
     min(event_type) OVER (PARTITION BY id ORDER BY ts ROWS BETWEEN 1 FOLLOWING AND 1 FOLLOWING) = 'Event B' 
    ) OR 
    (
     event_type = 'Event B' 
     AND 
     max(event_type) OVER (PARTITION BY id ORDER BY ts ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) = 'Event A' 
    ); 

+------+---------------+-------------+------------+ 
| id |  ts  | location | event_type | 
+------+---------------+-------------+------------+ 
| 1111 | 20160601-0112 | Detroit  | Event A | 
| 1111 | 20160602-0954 | Brooklyn | Event B | 
| 1113 | 20161124-1841 | New Orleans | Event A | 
| 1113 | 20161124-2100 | New Orleans | Event B | 
+------+---------------+-------------+------------+