Question

这是我的代码

select c.number as num, 
       convert(varchar,c.datestart,101) as date_start,  
       convert(varchar,max(c.datestop),101) as date_stop, 
       c.name as name_ua, 
       cEng.name as name_eng, 
       cRus.name as name_rus, 
       citytype as city_type  
from cd_city c
left join dbo.cd_cityforeign cEng on cEng.city = c.number and cEng.language =1
left join dbo.cd_cityforeign cRus on cRus.city = c.number and cRus.language =2
order by c.number;

我已经阅读了一些解决我的问题的方法，但是对我没有帮助，例如带有group by的变量对我不起作用，我不知道为什么... 我试图通过子查询来做到这一点，但我是初学者，所以我犯了一些错误... 帮帮我，伙计们！也许我可以使用HAVING，但我仍然需要您的帮助来向我展示如何写...谢谢！让我们为您提供更多信息，当我尝试仅查找stopdates的最大值时出现此错误。

Answer 1

您正在使用不带GROUP BY的Aggregator MAX函数。但是您可以使用以下内联子查询来获得所需的结果。

SELECT c.number AS num, 
       CONVERT(VARCHAR, c.datestart, 101) AS date_start, 
       CONVERT(VARCHAR, (SELECT MAX(c2.datestop) FROM cd_city c2 WHERE c2.number = c.number), 101) AS date_stop, 
       c.name AS name_ua, 
       cEng.name AS name_eng, 
       cRus.name AS name_rus, 
       citytype AS city_type
FROM cd_city c
     LEFT JOIN dbo.cd_cityforeign cEng ON cEng.city = c.number
                                          AND cEng.language = 1
     LEFT JOIN dbo.cd_cityforeign cRus ON cRus.city = c.number
                                          AND cRus.language = 2
ORDER BY c.number;

另一个选择。你能检查这个对你有用吗？

SELECT c.number AS num, 
       convert(varchar,MIN(c.datestart),101) as date_start,  
       convert(varchar,max(c.datestop),101) as date_stop,
       c.name AS name_ua, 
       cEng.name AS name_eng, 
       cRus.name AS name_rus, 
       citytype AS city_type
FROM cd_city c
     LEFT JOIN dbo.cd_cityforeign cEng ON cEng.city = c.number
                                          AND cEng.language = 1
     LEFT JOIN dbo.cd_cityforeign cRus ON cRus.city = c.number
                                          AND cRus.language = 2
GROUP BY c.number, 
        c.[name], 
       cEng.[name], 
       cRus.[name], 
       citytype
ORDER BY c.number;

Answer 2

您应该写MAX(c.datestop)而不是MAX(c.datestop) OVER ()作为整体最大值。如果您需要每个c.number的最大值，请写MAX(c.datestop) OVER (PARTITION BY c.number) 因此，您的查询将如下所示：

SELECT c.number   AS num,
       CONVERT(VARCHAR, c.datestart, 101) AS date_start,
       CONVERT(VARCHAR, MAX(c.datestop) OVER (PARTITION BY c.number), 101) AS date_stop,
       c.name     AS name_ua,
       cEng.name  AS name_eng,
       cRus.name  AS name_rus,
       citytype   AS city_type
FROM   cd_city c
       LEFT JOIN dbo.cd_cityforeign cEng
            ON  cEng.city = c.number
            AND cEng.language = 1
       LEFT JOIN dbo.cd_cityforeign cRus
            ON  cRus.city = c.number
            AND cRus.language = 2
ORDER BY
       c.number

这称为窗口函数，该函数可帮助您聚合数据而无需使用group by子句的子查询。有关更多信息，请访问https://docs.microsoft.com/ru-ru/sql/t-sql/queries/select-over-clause-transact-sql?view=sql-server-2017

选择列表中的列“ c.number”无效，因为它既不包含在聚合函数中也不在GROUP BY子句中

2 个答案: