[英]How to find max value of column with NULL being included and considered the max
我有一張帶有一列日期的表,其中包括日期和NULL
值。 我試圖找出一種方法來找到每個ID
的MAX Date
,或者如果有NULL
值,則返回NULL
。
因此,例如:
ID Date
1 2014-01-01
1 2014-02-01
1 2014-03-01
2 2014-02-01
2 NULL
3 NULL
4 2014-03-01
所以我想產生的是:
1 = 2014-03-01
2 = NULL
3 = NULL
4 = 2014-03-01
截至目前,我使用的是這樣的東西:
NULLIF(MAX(COALESCE(n.[SentDate], '12/16/9997')),'12/16/9997') AS [MaxSentDate]
我有99%的把握確保不會有人將日期定為12/16/9997
,但是我想提出一種適當的解決方案,而不是使用像這樣的12/16/9997
解決方案。
嘗試這個 :
SELECT [ID]
, CASE WHEN MAX(CASE WHEN [Date] IS NULL THEN 1 ELSE 0 END) = 0 THEN MAX([Date]) END
FROM YourTable
GROUP BY [ID]
SELECT ID, [Date]
FROM (
SELECT ID
,[DATE]
,ROW_NUMBER() OVER (PARTITION BY ID ORDER BY CASE WHEN [Date] IS NULL
THEN '99991212'
ELSE [Date] END DESC) RN
FROM TABLE_NAME) A
WHERE RN = 1
Working SQL FIDDLE
如果要返回null:
SELECT id, max([date]) from #t t1
WHERE not exists (select 1 from #t t2 where t2.date is null and t1.id = t2.id)
GROUP BY id
UNION ALL
SELECT id, NULL from #t t1
WHERE t1.date IS NULL
GROUP BY id ;
您可以使用COUNT(*) = COUNT([DATE])
來檢查組中是否為空(右側部分返回COUNT
,表示該組中的所有值,左側部分僅返回非空值):
SELECT [ID]
, CASE WHEN COUNT(*) = COUNT([DATE]) THEN MAX([DATE]) ELSE NULL END AS [DATE]
FROM [TEST_TABLE]
GROUP BY [ID]
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