SQL UPDATE with multiple WHERE (relations) conditions - sql

Question

I would like to know if it is possible to perform such UPDATE in oracle SQL database :
UPDATE mark
SET
mark=
CASE
WHEN mark.val<= 5
THEN val*1.1
ELSE val END
WHERE mark.id_classes = classes.id_classes
AND classes.ID_subject = subject.ID_subject
AND subject.ID_subject = 5;
SQL developer returns error in this part :
WHERE mark.id_classes = classes.id_classes
AND classes.ID_subject = subject.ID_subject
AND subject.ID_subject = 5;
So I guess that it is not possible to make such a complex condition, is it any other way to do that then?
Might be silly to try more SELECT like condition but on the other hand I don't see the reason why it is not working.

Answer 1

You can use a subquery:
UPDATE mark
SET mark = val * 1.1
WHERE mark.val <= 5 AND
EXISTS (SELECT 1
FROM classes c JOIN
subjects s
ON c.ID_subject = s.ID_subject
WHERE mark.id_classes = c.id_classes AND
s.ID_subject = 5
);
Notice that I moved the CASE condition to the WHERE clause so only the rows that need to be updated are updated.

Answer 2

You can't reference another two tables (CLASSES and SUBJECT) just like that, out of nowhere. Here's code which shows how you might have done that:
update mark m set
m.mark = (select case when m.val <= 5 then m.val * 1.1
else m.val
end
from classes c join subject s on c.id_subject = s.id_subject
where c.id_classes = m.id_classes
and s.id_subject = 5
)
where ...
As you didn't use table aliases within CASE, I don't know which table the VAL column belongs to (so I presumed it is MARK).
Also, UPDATE itself might need the WHERE clause which would restrict number of rows to be updated.

Answer 3

I find that in cases like this a MERGE statement is easier to understand:
MERGE INTO MARK m
USING (SELECT c.ID_CLASSES
FROM CLASSES c
WHERE c.ID_SUBJECT = 5) d
ON (m.ID_CLASSES = d.ID_CLASSES)
WHEN MATCHED THEN
UPDATE SET m.MARK = CASE
WHEN m.VAL <= 5
THEN m.VAL * 1.1
ELSE
m.VAL
END
Or, since the ID_SUBJECT is a constant, you can simplify your update to
UPDATE MARK m
SET m.MARK = CASE
WHEN m.VAL <= 5
THEN m.VAL * 1.1
ELSE
m.VAL
END
WHERE m.ID_CLASSES = 5
Best of luck.