Question

我有一个查询，我正在寻找4个表的结果：客户端，客户计划，INSPLANS和CLIENTLOG 我的查询从表中提取了更多信息，但简化了如下：

select clients.name,
       insplans.desc,
       clientplans.group_no,
       convert (varchar,clientlog.FNDATE,112) as LASTUPDATEDATE,
FROM 
       PROJECT.DBO.CLIENTS
join CLIENTPLANS
       on clients.RECORD_ID = clientplans.CLIENT_ID
join INSPLANS
       on insplans.RECORD_ID = clientplans.PLAN_ID
join CLIENTLOG
       on clientlog.CLIENT_ID = clients.RECORD_ID
WHERE clients.record_id = clientplans.client_id
       and clientplans.SEQUENCE_NUM < 2

我的问题是，当我加入CLIENTLOG表时，我的结果会从3k气球中消失，预计会有33K重复数据。 clientlog表显示对clients表进行的每次更新的条目。我只是想获得最后更新日期的记录。我知道我应该通过转换函数使用MAX，但我有一种感觉，我加入表的方式也是不正确的。如果有人能提供一些令人敬畏的澄清。

由于

Answer 1

试试这个..

SELECT clients.NAME, 
       insplans.desc, 
       clientplans.group_no, 
       CONVERT (VARCHAR, clientlog.fndate, 112) AS LASTUPDATEDATE, 
FROM   project.dbo.clients 
       JOIN clientplans 
         ON clients.record_id = clientplans.client_id 
       JOIN insplans 
         ON insplans.record_id = clientplans.plan_id 
       JOIN (SELECT Max(fndate) FNDATE, 
                    client_id 
             FROM   clientlog 
             GROUP  BY clientid) CLIENTLOG 
         ON clientlog.client_id = clients.record_id 
WHERE  clients.record_id = clientplans.client_id 
       AND clientplans.sequence_num < 2

Answer 2

您可以使用MAX添加获取最新的FnDate，您只需要将您选择的其他列添加到GROUP BY子句中：

SELECT  clients.name,
        insplans.desc,
        clientplans.group_no,
        CONVERT(VARCHAR(8), MAX(clientlog.FNDATE), 112) AS LASTUPDATEDATE
FROM    PROJECT.DBO.CLIENTS
        INNER JOIN CLIENTPLANS
           ON clients.RECORD_ID = clientplans.CLIENT_ID
        INNER JOIN INSPLANS
           ON insplans.RECORD_ID = clientplans.PLAN_ID
        INNER JOIN CLIENTLOG
           ON clientlog.CLIENT_ID = clients.RECORD_ID
WHERE   clientplans.SEQUENCE_NUM < 2
GROUP BY clients.name,insplans.desc, clientplans.group_no;

这里实际上没有什么区别，但specify a length when declaring, or converting to a VARCHAR

是一种好习惯

加入3个表并从一个表中获取上次更新日期

2 个答案: