Question

I read Create a Cumulative Sum Column in MySQL, and tried to adapt it to what I’m doing, but I can’t seem to get it right.

The table:

Id (primary key)
AcctId
CommodId
Date
PnL

There is a unique index which contains AcctId, CommodId, Date. I want to get a cumulative total grouped by date.

This query

select c.date
   , c.pnl
   ,(@cum := @cum + c.pnl) as "cum_pnl"
   from commoddata c join (select @cum := 0) r
   where
   c.acctid = 2
   and
   c.date >= "2011-01-01"
   and
   c.date <= "2011-01-31"
   order by c.date

will correctly calculate the running total for all records, showing data in the format

date        pnl       cum_pnl
========    ======    =======
2011-01-01       1          1
2011-01-01       1          2
2011-01-01       1          3
2011-01-01       1          4
2011-01-02       1          5
2011-01-02       1          6
...

(there can be many records per date). What I want is

date        cum_pnl
========    =======
2011-01-01       4
2011-01-02       6
...

But nothing I’ve tried works. TIA.

Answer 1

Alternately I think you can replace all your pnl with sum(pnl), and let your @cum run across those. I think it would look like this:

select c.date
   ,SUM(c.pnl)
   ,(@cum := @cum + SUM(c.pnl)) as "cum_pnl"
   from commoddata c join (select @cum := 0) r
   where
   c.acctid = 2 and c.date >= "2011-01-01" and c.date <= "2011-01-31"
   order by c.date
   GROUP BY c.date

I’m just trying to figure out if SQL will give you grief over selecting cum_pnl when it is not a group by expression… maybe you can try grouping by it as well?

EDIT New Idea, if you’re really not averse to nested queries, replace commoddata with a summed grouped query

select c.date
   ,c.pnl
   ,(@cum := @cum + c.pnl) as "cum_pnl"
   from 
       (SELECT date, sum(pnl) as pnl FROM commoddata WHERE [conditions] GROUP BY date) c 
       join (select @cum := 0) r
   order by c.date