DB2 LUW MERGE 使用相同的 table 来更新不同的行

Question

我的 table 数据是这样的

我的拙劣尝试SQL是这个...

MERGE INTO PRINT target  
USING  
(  
    select ID,PDF_FILE   
    from PRINT  
    where date(PRINTED) = '2022-01-06'  
      and PDF_FILE is not null  
) sause  
ON (target.ID = sause.ID)  
WHEN MATCHED THEN  
    UPDATE SET target.PDF_FILE = sause.PDF_FILE

它正在更新 table 中的所有行。我不要这个。

我怎样才能让它只更新 1 个空 PDF_FILE 的最新 PRINTED 行？

Answer 1

想法是枚举目标行并仅更新第一行。

MERGE INTO 
(
SELECT ID, PDF_FILE, ROW_NUMBER () OVER (PARTITION BY ID ORDER BY PRINTED DESC) AS RN_ 
FROM PRINT
WHERE
-- Below is an appropriate condition for
-- the target rows to distinguish them from the source row

-- PDF_FILE IS NULL
date (PRINTED) <> '2022-01-06'
) target
USING
(
select ID,PDF_FILE
from PRINT
where date (PRINTED) = '2022-01-06'
and PDF_FILE is not null
) sause
ON target.ID = sause.ID AND target.RN_ = 1 
WHEN MATCHED THEN
UPDATE SET target.PDF_FILE = sause.PDF_FILE

DB2 LUW MERGE 使用相同的 table 来更新不同的行

DB2 LUW MERGE using same table to update a different row

sql

merge

db2-luw