在SQL SERVER中使用ISNULL更新查询

Question

DateTime如果传递了数据，则应更新；否则，将其更新为已保存的原始值。 此更新不起作用

DECLARE @FolderStatusDate DATETIME = NULL

SET @FolderStatusDate = '2012-07-04 14:09:04.043'

UPDATE CM.PfmFolder     
  SET   
      FolderStatusDate = ISNULL(@FolderStatusDate, FolderStatusDate)
      WHERE Id = @Id  

Answer 1

为什么不将NULL检查移到WHERE子句？

DECLARE @FolderStatusDate DATETIME = NULL

SET @FolderStatusDate = '2012-07-04 14:09:04.043'

UPDATE CM.PfmFolder     
  SET   
      FolderStatusDate = @FolderStatusDate
      WHERE Id = @Id  
      AND @FolderStatusDate IS NOT NULL

Answer 2

你也可以这样

DECLARE @FolderStatusDate DATETIME = NULL

SET @FolderStatusDate = '2012-07-04 14:09:04.043'

UPDATE CM.PfmFolder     
SET   
  FolderStatusDate = case when ISNULL(@FolderStatusDate, '') = '' 
                           then FolderStatusDate else @FolderStatusDate end
  WHERE Id = @Id

Answer 3

对Hitesh Salian的答案进行略微修改

 DECLARE @FolderStatusDate DATETIME = NULL

 SET @FolderStatusDate = '2012-07-04 14:09:04.043'

 UPDATE CM.PfmFolder     
 SET   
 FolderStatusDate = case @FolderStatusDate is Null
                       then FolderStatusDate else @FolderStatusDate end
 WHERE Id = @Id