MySQL query that computes partial sums

Question

What query should I execute in MySQL database to get a result containing partial sums of source table?

For example when I have table:

Id|Val
1 | 1
2         


        

Answer 1

You can do this by joining the table on itself. The SUM will add up all rows up to this row:

select cur.id, sum(prev.val)
from TheTable cur
left join TheTable prev
    on cur.id >= prev.id
group by cur.id

MySQL also allows the use of user variables to calculate this, which is more efficient but considered something of a hack:

select 
     id
,    @running_total := @running_total + val AS RunningTotal
from TheTable