SQL Server：在 CASE 表达式后排除具有 NULL 值的行

Question

下面的查询以我想要的方式聚合来自日志记录表的数据...

SELECT 
    [TransactionNumber]
    ,MIN(CASE WHEN [Entry] = 'Updated status to Awaiting OCLC Sending' THEN [DateTime] END) AS 'start' 
    ,MAX(CASE WHEN [Entry] = 'Updated Status to: Delivered to Web' THEN [DateTime] END) AS 'end' 
    FROM [ILLData].[dbo].[History]
    GROUP BY [TransactionNumber] 
    /*
    227882  2015-09-29 14:17:07.443 2015-09-29 15:27:03.180
    227883  NULL    NULL
    227884  2015-09-29 14:29:22.340 NULL
    227885  NULL    2015-09-29 14:59:54.677
    */

...但我想排除任何包含 NULL 值的结果行。我尝试了下面的查询，但我一直得到相同的结果，并且没有排除具有 NULL 值的行。

SELECT 
    [TransactionNumber]
    ,MIN(CASE WHEN [Entry] = 'Updated status to Awaiting OCLC Sending' THEN [DateTime] END) AS 'start' 
    ,MAX(CASE WHEN [Entry] = 'Updated Status to: Delivered to Web' THEN [DateTime] END) AS 'end' 
FROM 
    [ILLData].[dbo].[History]
WHERE 
    'start' IS NOT NULL 
    AND 'end' IS NOT NULL 
GROUP BY 
    [TransactionNumber] 

/* still get rows with NULL values */

SELECT 
    [TransactionNumber]
    ,MIN(CASE WHEN [Entry] = 'Updated status to Awaiting OCLC Sending' THEN [DateTime] END) AS 'start' 
    ,MAX(CASE WHEN [Entry] = 'Updated Status to: Delivered to Web' THEN  [DateTime] END) AS 'end' 
FROM 
    [ILLData].[dbo].[History] 
GROUP BY  
    [TransactionNumber] 
HAVING 
    'start' IS NOT NULL 
    AND 'end' IS NOT NULL

/* still get rows with NULL values */

WITH history AS 
(
   SELECT  
       [TransactionNumber]
       ,MIN(CASE WHEN [Entry] = 'Updated status to Awaiting OCLC Sending' THEN [DateTime] END) AS 'start' 
       ,MAX(CASE WHEN [Entry] = 'Updated Status to: Delivered to Web' THEN [DateTime] END) AS 'end' 
   FROM 
       [ILLData].[dbo].[History]
   GROUP BY 
       [TransactionNumber])
SELECT * 
FROM history 
WHERE 'start' IS NOT NULL 
  AND 'end' IS NOT NULL 

/* still get rows with NULL values */

有没有办法过滤我使用CASE的查询结果？

Answer 1

问题在于您的字段名称，因为“开始”永远不会为空，因为 SQL 将文本值与空值进行比较。稍有改变，您的查询就可以了。

SELECT *
FROM
(SELECT 
[TransactionNumber]
,MIN(CASE WHEN [Entry] = 'Updated status to Awaiting OCLC Sending' THEN [DateTime] END) AS [start] 
,MAX(CASE WHEN [Entry] = 'Updated Status to: Delivered to Web' THEN [DateTime] END) AS [end] 
FROM [ILLData].[dbo].[History]
GROUP BY [TransactionNumber]) x
WHERE [start] IS NOT NULL 
AND [end] IS NOT NULL