CASE表达式返回NULL值

Question

I am trying to get status of my tickets using case expression. It's working perfectly but not returning Not Available . Rather than that it's returning a null value in Status as result.

What's wrong with this query?

Secondly can I make further if else on returning of operations?

Select 
Case 
      When Status=1 and isTaken=1 then 'Open'
      When Status=4 and isTaken=0 then 'Expire'
      When Status=2 and isTaken=0 then 'Pending'
      When Status=0 and isTaken=0 then 'Close'

Else 'Not Available' End As 'Status' 
from Tickets 
Where Id='1234567890'

Check Image for more explanation.

Answer 1

Your query is not returning NULL , it's returning 0 rows. Your WHERE is filtering the rows or your table is empty.

Remove the WHERE and see if it returns rows, to see if the table isn't empty. If so then make sure that your ID filter is correct.

If your want to return a row even if the filter doesn't find anything then you need a NOT EXISTS or a LEFT JOIN :

DECLARE @ID VARCHAR(20) = '1234567890'

SELECT
    F.ID,
    Case 
        When Status=1 and isTaken=1 then 'Open'
        When Status=4 and isTaken=0 then 'Expire'
        When Status=2 and isTaken=0 then 'Pending'
        When Status=0 and isTaken=0 then 'Close'
    Else 'Not Available' End As 'Status' 
FROM
    (VALUES (@ID)) AS F(ID)
    LEFT JOIN Tickets AS C ON F.ID = C.Id