Question

I have the following UPDATE statement:

update MESSAGES set status=
    (select (CASE 
               WHEN from_id='111111111' 
               THEN (CASE 
                      WHEN status='A' 
                      THEN 'S' 
                  WHEN status='R' 
                      THEN 'D' 
                     END)
               WHEN to_id='111111111' 
               THEN (CASE 
                       WHEN status='A' 
                       THEN 'R' 
                   WHEN status='S' 
                       THEN 'D' 
                     END) 
             END)
    as status_value)
where primary_key='236499681204' 
and status_value not null ;

The problem with this query is, at the last line, status_value is not recognized. If I remove the last comparison, and status_value not null, it works. I dint expect the above version to work, but could someone tell me an alternative that would achieve the same?

Is there a way I can use the AS keyword in the UPDATE query to define the variable status_value?

Edit

The actual requirement is not just that i check if status_value is null, but also that I dont perform any update if it is null

Answer 1

Try to add ELSE STATUS and remove and status_value not null:

  update MESSAGES set status=
    (select (CASE 
               WHEN from_id='111111111' 
               THEN (CASE 
                      WHEN status='A' 
                      THEN 'S' 
                  WHEN status='R' 
                      THEN 'D' 
                     END)
               WHEN to_id='111111111' 
               THEN (CASE 
                       WHEN status='A' 
                       THEN 'R' 
                   WHEN status='S' 
                       THEN 'D' 
                     END) 
             ELSE STATUS 
             END)
    as status_value)
where primary_key='236499681204'; 

You can also try to use view

create view MyView as
select (CASE 
               WHEN from_id='111111111' 
               THEN (CASE 
                      WHEN status='A' 
                      THEN 'S' 
                  WHEN status='R' 
                      THEN 'D' 
                     END)
               WHEN to_id='111111111' 
               THEN (CASE 
                       WHEN status='A' 
                       THEN 'R' 
                   WHEN status='S' 
                       THEN 'D' 
                     END) 
             END)
    as status_value;

update MESSAGES set status= mv.status_value
from MyView mv
where primary_key='236499681204'
and mv.status_value is null

or you can use case in condition

 update MESSAGES set status=
    (select (CASE 
               WHEN from_id='111111111' 
               THEN (CASE 
                      WHEN status='A' 
                      THEN 'S' 
                  WHEN status='R' 
                      THEN 'D' 
                     END)
               WHEN to_id='111111111' 
               THEN (CASE 
                       WHEN status='A' 
                       THEN 'R' 
                   WHEN status='S' 
                       THEN 'D' 
                     END) 
             END)
    as status_value)
where primary_key='236499681204'
and CASE
     WHEN from_id='111111111' 
      THEN (CASE 
             WHEN status='A' 
             THEN 'S' 
             WHEN status='R' 
             THEN 'D' 
            END)
     WHEN to_id='111111111' 
      THEN (CASE 
             WHEN status='A' 
             THEN 'R' 
             WHEN status='S' 
             THEN 'D' 
            END) 
    END is not null;