如何在 Oracle 中使用带有 CASE 语句的更新命令？

Question

我必须根据以下条件更新匹配标志列：

当 F_ZN=IC_ZN AND F_STN=IC_STN 然后 Matching Flag 将设置为 1 else 0 ，我可以想到这个，但我不知道确切的语法。

UPDATE F_STATE_MAPPING SET MATCHING_FLAG=CASE WHEN F_ZN=IC_ZN AND F_STN=IC_STN THEN 1 ELSE 0 END  
FROM 
(
SELECT F_ZN,F_STN,IC_ZN,IC_STN FROM 
(
SELECT A.ZN_CD AS F_ZN,A.STN AS F_STN,B.ZN_CD AS IC_ZN,B.STN AS IC_STN FROM 
F_STATE_MAPPING A,TEMP_STN_STATE_MAPPING B WHERE A.ZN_CD=B.ZN_CD AND A.STN=B.STN
)
)

F_STATE_MAPPING 表的架构是

    ZN_CD VARCHAR2(4)
    STN   VARCHAR2(4) 
MATCHING_FLAG NUMBER(1)

请指导。

Answer 1

你要不要使用exists？

UPDATE F_STATE_MAPPING
    SET MATCHING_FLAG = (CASE WHEN EXISTS (SELECT 1
                                           FROM TEMP_STN_STATE_MAPPING
                                           WHERE F_ZN = IC_ZN AND F_STN = IC_STN
                                          )
                              THEN 1 ELSE 0
                         END) ;

Answer 2

如果要更新表的列，它必须首先存在：

ALTER TABLE F_STATE_MAPPING ADD  MATCHING_FLAG int

那你就可以更新了

UPDATE 
(
    SELECT A.MATCHING_FLAG,
            CASE WHEN (A.ZN_CD=B.ZN_CD AND A.STN=B.STN) THEN 1 ELSE 0 END AS NEWVALUE
    FROM F_STATE_MAPPING A 
    LEFT JOIN TEMP_STN_STATE_MAPPING B ON A.ZN_CD=B.ZN_CD AND A.STN=B.STN
) t
SET t.MATCHING_FLAG = t.NEWVALUE

也可以写成：

 UPDATE 
    (
        SELECT A.MATCHING_FLAG,
                CASE WHEN (B.ZN_CD is null) THEN 0 ELSE 1 END AS NEWVALUE
        FROM F_STATE_MAPPING A 
        LEFT JOIN TEMP_STN_STATE_MAPPING B ON A.ZN_CD=B.ZN_CD AND A.STN=B.STN
    ) t
    SET t.MATCHING_FLAG = t.NEWVALUE