比較previus行設​​置「StatusFlag」

Question

我想比較我的表中「ExtractTypeNum」的前一行。所以如果它從之前的標誌更改爲「isChanged」。

我試圖用case語句來開發，但沒有任何成功。

select * 
    (case 
     when rownum = rownum-1 
      then 
       (case when 
       extractTypeNum <> extractTypeNum 
        then Null 
        else 'IsChanged' end) 
      when rownum = rownum -'1' then '3' 
     else '4' end) as StatusFlag 
from myTable 

這是表的結構和一些樣本數據：

CREATE TABLE mytable(
    ExtractTypeNum INTEGER NOT NULL PRIMARY KEY 
    ,FileOrderNum  VARCHAR(11) NOT NULL 
    ,PrevFileOrderNum VARCHAR(11) NOT NULL 
    ,NextFileOrderNum VARCHAR(11) NOT NULL 
    ,rownum1   INTEGER NOT NULL 
    ,Statusflag1  VARCHAR(9) NOT NULL 
); 
INSERT INTO mytable(ExtractTypeNum,FileOrderNum,PrevFileOrderNum,NextFileOrderNum,rownum1,Statusflag1) 
VALUES (1,'2016-09-191',NULL,'2016-09-192',1,'IsInitial'); 
INSERT INTO mytable(ExtractTypeNum,FileOrderNum,PrevFileOrderNum,NextFileOrderNum,rownum1,Statusflag1) 
VALUES (2,'2016-09-192','2016-09-191','2016-09-201',2,NULL); 
INSERT INTO mytable(ExtractTypeNum,FileOrderNum,PrevFileOrderNum,NextFileOrderNum,rownum1,Statusflag1) 
VALUES (1,'2016-09-201','2016-09-192','2016-09-211',3,NULL); 
INSERT INTO mytable(ExtractTypeNum,FileOrderNum,PrevFileOrderNum,NextFileOrderNum,rownum1,Statusflag1) 
VALUES (1,'2016-09-211','2016-09-201','2016-09-222',4,NULL); 
INSERT INTO mytable(ExtractTypeNum,FileOrderNum,PrevFileOrderNum,NextFileOrderNum,rownum1,Statusflag1) 
VALUES (2,'2016-09-222','2016-09-211',NULL,5,'IsLatest'); 

Expected output 
+----------------+--------------+------------------+------------------+--------+-------------+ 
| ExtractTypeNum | FileOrderNum | PrevFileOrderNum | NextFileOrderNum | rownum | Statusflag1 | 
+----------------+--------------+------------------+------------------+--------+-------------+ 
|    1 | 2016-09-191 | NULL    | 2016-09-192  |  | IsInitial | 
|    2 | 2016-09-192 | 2016-09-191  | 2016-09-201  |  | IsChanged | 
|    1 | 2016-09-201 | 2016-09-192  | 2016-09-211  |  | IsChanged | 
|    1 | 2016-09-211 | 2016-09-201  | 2016-09-222  |  | NULL  | 
|    2 | 2016-09-222 | 2016-09-211  | NULL    |  | IsLatest | 
+----------------+--------------+------------------+------------------+--------+-------------+ 

Answer 1

如果您正在使用SQL Server 2012或更高版本，那麼你可以嘗試以下查詢：

;WITH CTE AS (
    SELECT ExtractTypeNum, FileOrderNum, PrevFileOrderNum, 
      NextFileOrderNum, rownum1, Statusflag1, 
      ROW_NUMBER() OVER (ORDER BY rownum1) AS rn, 
      COUNT(*) OVER() AS totalCnt, 
      LAG(ExtractTypeNum) OVER (ORDER BY rownum1) AS prevExtractTypeNum    
    FROM mytable 
) 
SELECT ExtractTypeNum, FileOrderNum, PrevFileOrderNum, 
     NextFileOrderNum, rownum1, Statusflag1, 
     CASE 
      WHEN rn = 1 THEN 'IsInitial' 
      WHEN rn = totalCnt THEN 'IsLatest' 
      WHEN prevExtractTypeNum <> ExtractTypeNum THEN 'IsChanged' 
     END AS StatusFlag 
FROM CTE