SQL - GROUP BY和COALESCE的丑陋組合

Question

我有一個表格，其數據類似於以下內容：

[ID]，[州]，[foo]，[DateCreated]，[DateUpdated]

我在這方面工作的時間越長，我的SQL就會變得更加丑陋，這告訴我，我可能做錯了什么。 我想要的是每個國家的唯一清單，只要該國的foo總是相同的（如果foo對於該州的所有記錄都不相同，我根本不想要那個國家） 。 此外，我想要COALESCE DateCreated和DateUpdated，並希望該狀態的最大值。

所以給出這樣的數據：

[ID], [State], [foo], [DateCreated], [DateUpdated]
1,  MA, data1,  05/29/2012, 06/02/2012
2,  MA, data1,  05/29/2012, 06/03/2012
3,  RI, data2,  05/29/2012, NULL
4,  RI, data3,  05/29/2012, NULL
5,  NH, data4,  05/29/2012, NULL
6,  NH, data4,  05/29/2012, 06/05/2012

我只想要這些結果：

[State], [foo], [LastUpdated]
MA, data1,  06/03/2012
NH, data4,  06/05/2012

得到我所追求的最優雅的方法是什么？

Answer 1

另一個：

http://sqlfiddle.com/#!6/fd219/1

SELECT
  t.State,
  MAX(t.foo),
  MAX( COALESCE( t.DateUpdated, t.DateCreated ))
FROM t
GROUP BY t.State
HAVING COUNT(DISTINCT t.foo) = 1;

Answer 2

使用嵌套查詢的簡單Group by就足夠了：

Select State, coalesce(max_created,max_updated) from (
  Select State, min(foo) as min_foo, max(foo) as max_foo, 
    max(DateCreated) as max_created,
    max(DateUpdated) as max_updated
  From Data
  Group by State)
 Where min_foo = max_foo

Answer 3

不那么優雅，但對於你可憐的SQL 2000靈魂：

SELECT T1.State, T2.Foo, T1.LastUpdated
FROM (
    SELECT State, MAX([ID]) AS [ID], 
        MAX(COALESCE(DateUpdated, DateCreated)) AS LastUpdated
    FROM YourTable
    GROUP BY State
    HAVING COUNT(DISTINCT Foo) = 1
) T1 
INNER JOIN YourTable T2 ON T1.State = T2.State AND T1.[ID] = T2.[ID]

Answer 4

假設您使用的是SQL Server 2005或>

試試這個：

WITH Data AS
(
    SELECT  *,
        COALESCE([DateCreated], [DateUpdated]) AS LastUpdated,
        ROW_NUMBER() OVER(PARTITION BY State ORDER BY COALESCE([DateCreated], [DateUpdated]) DESC) Position
      FROM <YOUR-TABLE> a
     WHERE NOT EXISTS
     (
        SELECT  1 
            FROM    <YOUR-TABLE> b
         WHERE  a.State = b.State
            AND a.foo <> b.foo
     )
)
SELECT State, foo, LastUpdated
  FROM Data
 WHERE Positon = 1

Answer 5

試試這個：

select state_name,foo,max(dateUpdated) from state where state_name in (select state_name from state group by state_name having count(distinct foo)=1) group by state_name,foo;