Question

我想比较表格中“ExtractTypeNum”的前一行。因此，如果它从前一个更改，则标志应设置为“isChanged”。

我试图通过案例陈述来开发这个但没有任何成功。

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

这是表的结构和一些示例数据：

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

如果您使用的是SQL Server 2012或更高版本，则可以尝试以下查询：

;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

比较previus行以设置“StatusFlag”

1 个答案: