update statement with aggregate function - mysql

Question

Good day everyone..!:-)
I have this table tab where totalUsed is equal to the sum of all used values referenced to name
cid name used total
1 a 1 1
2 a 3 4
3 a 6 10
4 b 3 3
5 b 7 10
6 b 10 0
7 a 5 0
i have this code but it only copy totalUsed's adjacent used value
UPDATE tab
SET totalUsed=
(
SELECT SUM(used)
)
cid name used total
1 a 1 1
2 a 3 3
3 a 6 6
4 b 3 3
5 b 7 7
6 b 10 10
7 a 5 5
if used is set as 10 for cid 6, totalUsed should be 20
and for cid 7 it should be 15.
how to do it in mysql?
it should look like this.
cid name used total
1 a 1 1
2 a 3 4
3 a 6 10
4 b 3 3
5 b 7 10
6 b 10 20
7 a 5 15
thanks for help
:-)

Answer 1

In most dialects of SQL, you can do this using an update with a correlated subquery:
UPDATE tab
SET totalUsed = (SELECT SUM(used)
from tab tab2
where tab2.name = tab.name and
tab2.cid <= tab.cid
);
EDIT:
The above will not work in MySQL. You can do this instead:
UPDATE tab join
(select tab2.cid,
(SELECT SUM(used)
from tab tab3
where tab3.name = tab2.name and
tab3.cid <= tab2.cid
) as cum_used
from tab tab2
) tab2
on tab.cid = tab2.cid
SET tab.totalUsed = tab2.cum_used;