SQLのどこの場所にある場合のケース

Question

DECLARE @ONum int --variable 
DECLARE @CrUsId nvarchar(128) = 'D901D15C-62FA-4243-A3DB-D3D448DC3F91'--assign value 

DECLARE @From Datetime = 4/2/2017 --assign value 
DECLARE @To Datetime = 25/2/2017 --assign value 

`declare @day nvarchar(50)` 
`select * from PurchaseOrder` 

where 
CreateUserID = CASE @CrUsId 
    WHEN @CrUsId = '' THEN CreateUserID 
WHEN @CrUsId <> CreateUserID THEN NULL -- if input is some text but  
    WHEN @CrUsId IS NULL THEN CreateUserID 
    WHEN @CrUsId != '' AND CreateUserID = @CrUsId THEN CreateUserID 
END 

Answer 1

これはあなたがやろうとしていることですか？

select * from PurchaseOrder 
    where CreateUserID = 
     CASE 
      WHEN @CrUsId = '' OR @CrUsId IS NULL THEN CreateUserID 
      WHEN @CrUsId <> CreateUserID THEN NULL -- if input is some text but  
      WHEN @CrUsId = CreateUserID THEN CreateUserID 
     END