在SQL SERVER中使用ISNULL更新查詢

Question

DateTime如果傳遞了數據，則應更新；否則，將其更新為已保存的原始值。 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

為什么不將NULL檢查移到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

你也可以這樣

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

對Hitesh Salian的答案進行略微修改

 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