Oracle SQL ROW_NUMBER（）窗口，其條件基於滯后

Question

使用Oracle SQL只選擇權限，我需要根據條件提供ROW_NUMBER輸出。 使用游標或循環這很容易，但目前我必須只使用SQL來執行此任務。

我一直在修補row_number() over子句，我認為這是正確的方法，但我現在卡住了。

我目前的代碼 - 或者至少是它的代理：

    WITH MYTABLE (FK_ID,FK_NAME,PK_ID,BIN_FLAG,MONTH,YEAR)AS (
      SELECT 10000,'VARCHAR DESCRIPTION',75057,1,1,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,1,2,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,1,3,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,4,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,1,5,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,6,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,7,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,1,8,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,9,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,10,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,1,11,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,12,2016 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,1,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,2,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,3,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,4,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,5,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,6,2017 FROM DUAL
UNION SELECT 10000,'VARCHAR DESCRIPTION',75057,0,7,2017 FROM DUAL

)

SELECT
   FK_ID
,  FK_NAME
,  PK_ID
,  BIN_FLAG
,  ROW_NUMBER() OVER (PARTITION BY FK_ID,PK_ID,BIN_FLAG ORDER BY YEAR,MONTH,FK_ID,PK_ID ASC) NEEDED_CALC
,  MONTH
,  YEAR
FROM MYTABLE
ORDER BY FK_ID,PK_ID,YEAR,MONTH

這將返回一個如下所示的數據集：

FK_ID   FK_NAME             PK_ID       BIN_FLAG    NEEDED_CALC MONTH   YEAR
10000   VARCHAR DESCRIPTION 75057       1           1           1       2016
10000   VARCHAR DESCRIPTION 75057       1           2           2       2016
10000   VARCHAR DESCRIPTION 75057       1           3           3       2016
10000   VARCHAR DESCRIPTION 75057       0           1           4       2016
10000   VARCHAR DESCRIPTION 75057       1           4           5       2016
10000   VARCHAR DESCRIPTION 75057       0           2           6       2016
10000   VARCHAR DESCRIPTION 75057       0           3           7       2016
10000   VARCHAR DESCRIPTION 75057       1           5           8       2016
10000   VARCHAR DESCRIPTION 75057       0           4           9       2016
10000   VARCHAR DESCRIPTION 75057       0           5           10      2016
10000   VARCHAR DESCRIPTION 75057       1           6           11      2016
10000   VARCHAR DESCRIPTION 75057       0           6           12      2016
10000   VARCHAR DESCRIPTION 75057       0           7           1       2017
10000   VARCHAR DESCRIPTION 75057       0           8           2       2017
10000   VARCHAR DESCRIPTION 75057       0           9           3       2017
10000   VARCHAR DESCRIPTION 75057       0           10          4       2017
10000   VARCHAR DESCRIPTION 75057       0           11          5       2017
10000   VARCHAR DESCRIPTION 75057       0           12          6       2017
10000   VARCHAR DESCRIPTION 75057       0           13          7       2017

我需要的是NEEDED_CALC列，以便在上個月的bin_flag改變時重置calc。

因此，如果bin_flag = 1且前一個月的bin_flag （通過lag函數識別）不同，則NEEDED_CALC的計數器列將重置並再次從1開始。

Answer 1

這是一個“差距和島嶼”問題。 關鍵是將組標識符分配給具有相同值的相鄰行。 有兩種簡單的方法可以做到這一點：一種是基於lag() ，另一種是row_number()的差異。

第二個是更簡單，只需要一個子查詢級別：

select t.*,
       row_number() over (partition by fk_id, bin_flag, seqnum_ym - seqnum_bym
                          order by year, month
                         ) as needed_calc
from (select t.*,
             row_number() over (partition by fk_id order by year, month) as seqnum_ym,
             row_number() over (partition by fk_id order by bin_flag, year, month) as seqnum_bym
      from mytable t
     ) t;

行數的差異並不難理解，但確實需要概念上的飛躍。 我建議您運行子查詢，看看seqnum_ym和seqnum_bym的值是什么，以了解它是如何工作的。

Answer 2

我很幸運能夠在12c數據庫上工作，你可以使用match recognition子句來完成這項工作。 在這種情況下，我告訴匹配引擎使用與問題中相同的順序查找其中bin_flag等於前一行的bin_flag的0行或更多行的組。

WITH MYTABLE (FK_ID,FK_NAME,PK_ID,BIN_FLAG,MONTH,YEAR)AS (
 <<<as from the question>>>> 
)
SELECT
 FK_ID 
,FK_NAME
,PK_ID
,BIN_FLAG
,seq NEEDED_CALC
,MONTH
,YEAR
FROM MYTABLE
MATCH_RECOGNIZE (
  ORDER BY year,month,fk_id,pk_id asc
  MEASURES
    count(*) +1 seq 
  ALL ROWS PER MATCH
  PATTERN (a*)
  DEFINE 
  a AS bin_flag = prev(bin_flag)
  )
ORDER BY FK_ID,PK_ID,YEAR,MONTH

匹配識別對於此類查詢而言是一種有用的工具，您可以在這些查詢中查找跨行組的模式。