SQL - Giving AS keyword in UPDATE Statement - mysql

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;

Answer 2

assuming all you want is to get rid of the null, you can do this:
update MESSAGES set status=
IFNULL(
(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),
status)
where primary_key='236499681204' ;

Answer 3

It seems to me that you're trying to do a sub-query for the update statement, when I don't think it's really all that necessary.
You can simplify the query a bit like this:
UPDATE MESSAGES
SET status = CASE
WHEN
(from_id='111111111' AND status='A') THEN 'S'
WHEN
(to_id ='111111111' AND status='A') THEN 'R'
WHEN
(from_id ='111111111' AND status='R') OR
(to_id ='111111111' AND status='S') THEN 'D'
ELSE status
END
WHERE priamry_key = '236499681204'