从查询返回空行

Question

我想知道是否有人能够帮助我处理我正在处理的DB2查询？

我基本上试图在Control Number上的两个表DB2Cust和NOTIFICATION_REQUE之间做左外连接。

我想返回DB2Cust中的所有行，但是，在NOTIFICATION_REQUE我想选择最大Notice_DT并仅返回该记录。

下面的查询是我到目前为止。

它很接近，但它不会返回DB2Cust中不存在的控制号码NOTIFICATION_REQUE。

SELECT 
    C.CONTROL_NO, 
    NR.CONTROL_NBR, 
    COALESCE(C.LNAME,'') AS LNAME, 
    COALESCE(C.FNAME,'') AS FNAME, 
    COALESCE(CAST(NR.NOTICE_DT AS VARCHAR(10)), '') AS NOTICE_DT 
FROM WITC00DS.DB2CUST C 
LEFT OUTER JOIN WITC00DS.NOTIFICATION_REQUE NR 
      ON C.CONTROL_NO = NR.CONTROL_NBR 
     AND C.AGENT_CODE = 'HR' AND C.STW_DATE BETWEEN '01/01/2000' AND '01/17/2014' 
WHERE NR.NOTICE_DT = (SELECT MAX(NOTICE_DT) 
         FROM WITC00DS.NOTIFICATION_REQUE ZZ 
         WHERE ZZ.CONTROL_NBR = C.CONTROL_NO) 

Answer 1

这里有两种选择。您可以将子查询移到on条款：

SELECT C.CONTROL_NO, NR.CONTROL_NBR, COALESCE(C.LNAME,'') AS LNAME, COALESCE(C.FNAME,'') AS FNAME, 
     COALESCE(CAST(NR.NOTICE_DT AS VARCHAR(10)), '') AS NOTICE_DT 
FROM WITC00DS.DB2CUST C LEFT OUTER JOIN 
    WITC00DS.NOTIFICATION_REQUE NR 
    ON C.CONTROL_NO = NR.CONTROL_NBR AND 
     C.AGENT_CODE = 'HR' AND 
     C.STW_DATE BETWEEN '01/01/2000' AND '01/17/2014' AND 
     NR.NOTICE_DT = (SELECT MAX(NOTICE_DT) 
         FROM WITC00DS.NOTIFICATION_REQUE ZZ 
         WHERE ZZ.CONTROL_NBR = C.CONTROL_NO 
         ) 

或者你可以明确的'WHERE子句中检查NULL：

SELECT C.CONTROL_NO, NR.CONTROL_NBR, COALESCE(C.LNAME,'') AS LNAME, COALESCE(C.FNAME,'') AS FNAME, 
     COALESCE(CAST(NR.NOTICE_DT AS VARCHAR(10)), '') AS NOTICE_DT 
FROM WITC00DS.DB2CUST C LEFT OUTER JOIN 
    WITC00DS.NOTIFICATION_REQUE NR 
    ON C.CONTROL_NO = NR.CONTROL_NBR AND 
     C.AGENT_CODE = 'HR' AND 
     C.STW_DATE BETWEEN '01/01/2000' AND '01/17/2014' AND 
WHERE NR.NOTICE_DT is null or 
     NR.NOTICE_DT = (SELECT MAX(NOTICE_DT) 
         FROM WITC00DS.NOTIFICATION_REQUE ZZ 
         WHERE ZZ.CONTROL_NBR = C.CONTROL_NO 
        );