在情况表达式中返回NULL：SQL Server 2008

Question

I have following case statement for check result set,

SELECT
    CASE
    WHEN EXISTS(
           select CE_Issuedate from t_Certificate
           where CE_CertID_pk = (select IT_certID_fk_ind from t_item
                                 where IT_rfileID_fk = '1482'
                                 group by IT_rfileID_fk) 
    ) 
    THEN  (select CE_Issuedate from t_Certificate
           where CE_CertID_pk = (select IT_certID_fk_ind from t_item
                                 where IT_rfileID_fk = '1482'
                                 group by IT_rfileID_fk)) 
    ELSE  NULL
    END AS 'CE_Issuedate';

I want to return NULL when no result in this select statement. I tried like this but I'm not sure this is correct. This query is working, but I think return string value when no result.

Following script return like this:

but i think actually it's want to be like this,

please help me. is this right ?

Answer 1

select max(CE_Issuedate)
from t_Certificate
where EXISTS (select * from t_item
              where IT_rfileID_fk = '1482'
                and CE_CertID_pk = IT_rfileID_fk)

If no row is found, MAX returns NULL. Otherwise that CE_Issuedate is returned.