1

Question

我试图从SQL Server中的3个表中获取所有不同的帐号，但似乎我的方式不起作用，有什么建议吗？

SELECT distinct account, max(date_added) as date_added FROM table_one group by account
union
SELECT distinct account, max(date_added) as date_added, FROM table_two group by account
union
SELECT distinct account, max(date_added) as date_added, FROM table_three group by account  order by account asc

Answer 1

1

SELECT account, MAX(date_added) AS date_added
FROM table_one
GROUP BY account
UNION
SELECT account, MAX(date_added) AS date_added
FROM table_two
GROUP BY account
UNION
SELECT account, MAX(date_added) AS date_added
FROM table_three
GROUP BY account
ORDER BY account ASC

2

SELECT account, MAX(date_added) AS date_added
FROM (
    SELECT account, date_added
    FROM table_one
    UNION ALL
    SELECT account, date_added
    FROM table_two
    UNION ALL
    SELECT account, date_added
    FROM table_three
) t
GROUP BY account
ORDER BY account ASC

Answer 2

生成一组数据，结合结果，然后获取每个帐户的最大日期。这会生成一个内联视图，我们可以从中获取不同的帐户和最大日期。

SELECT account, max(date_Added) as Date_Added from (
SELECT account date_Added FROM table_one 
union
SELECT account, date_added FROM table_two 
union
SELECT account, date_added FROM table_three) B
Group by account

Answer 3

select account, MAX(date_added) 
FROM (
    SELECT account, date_added FROM table_one 
    union
    SELECT account, date_added FROM table_two
    union
    SELECT account, date_added FROM table_three 
) X
group by account  
order by account asc

这个查询的作用是，它将来自一个记录集中所有三个表的所有数据联合起来，因此您可以使用它，因为它是一个表。想象一下，你有3个账户，1,2和3，并且有以下数据在这3个表中分布：

Table One
Account | Date Added
--------+-----------
    1   | 01-01-2015
    2   | 01-02-2015

Table Two
Account | Date Added
--------+-----------
    3   | 01-03-2015
    1   | 01-02-2015

Table Three
Account | Date Added
--------+-----------
    2   | 01-04-2015
    3   | 01-05-2015

所以在联合所有这三个表中的所有记录之后，我们得到了以下表格＆＃39; table＆＃39; （实际上它是存储在内存中的记录集）：

Union Data
Account | Date Added
--------+-----------
    1   | 01-01-2015
    2   | 01-02-2015
    3   | 01-03-2015
    1   | 01-02-2015
    2   | 01-04-2015
    3   | 01-05-2015

我们只为这个集合中的每个不同帐户选择帐户和最新的date_added，因此我们得到以下结果：

Result Data
Account | Date Added
--------+-----------
    1   | 01-02-2015
    2   | 01-04-2015
    3   | 01-05-2015

随意提出与此相关的任何其他问题。

Answer 4

如果您想要一个包含所有帐户的列表，并且每个帐户只出现一次，那么您可以执行以下操作：

select distinct account from table_one
union
select distinct account from table_two
union 
select distinct account from table_three

通过使用union，您将不会获得重复的行，并且由于您只选择了帐户，因此您只能获得每个帐户一次。

然而，目前还不清楚你在使用date_added列做了什么。

使用SQL Server选择与MAX（）的Distinct

4 个答案:

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