计算每个人的跑步总次数

I need to show the running total for each person in my database but I could only get the running total for all of them, so these are my tables on the pic

我需要在我的数据库中显示每个人的运行总数，但是我只能得到所有这些人的运行总数，所以这是我在pic上的表。

I already have this query:

我已经有了这个查询:

SELECT 
    id, 
    studno,
    if(type=0,amount,0)debit,
    if(type=1,amount,0)credit,
    if(type=0,@bal:=@bal+amount,@bal:=@bal-amount) runningTotal
FROM
(SELECT id, studno, amount, 0 type from tblPayables 
UNION ALL 
SELECT id, studno, amount, 1 type from tblPayments)s, (SELECT @bal:=0)b
ORDER BY studno, id, type;

but the thing is I can only come up to this result:

但问题是我只能得出这样的结果:

The highlighted number should be 50 since it's for a different studno

突出显示的数字应该是50，因为它是用于不同的研究项目

2 个解决方案

#1

You must write your query in such a way that the variable is initialized every time an Id changes.

您必须以这样的方式编写查询:每次Id更改时，都会对变量进行初始化。

Let's say you can write a query or view with the following columns:

假设您可以使用以下列编写查询或视图:

id | studno | debit | credit
---+--------+-------+-------

So, let's write the query:

那么，让我们来写这个查询:

select id, debit, credit
     , @bal := ( -- If the value of the column `studno` is the same as the
                 -- previous row, @bal is increased / decreased;
                 -- otherwise, @bal is reinitialized
         case 
             when @studno = studno then @bal + debit - credit
             else debit - credit
         end
     ) as balance
     @studno := a.studno as studno -- It's important to update @studno
                                   -- AFTER you update @bal
from 
    (
        select @bal := 0
             , @studno := 0 -- This variable will hold the previous
                            -- value of the `studno` column
    ) as init, -- You must initialize the variables
    ( -- The above mentioned query or view
        select ...
        from ...
    ) as a
order by a.studno, a.id -- It's REALLY important to sort the rows

#2

as I wrote in comments - existing query does interleaving wrong, it will fail if payment id for corresponding payable id is smaller

正如我在comments中所写的那样——现有查询确实存在交叉错误，如果对应的应付id的支付id较小，那么它将失败

here is query which does interleaving properly and calculate running total as @Barranka suggested:

这里有一个查询，它正确地交错并按照@Barranka的建议计算运行总量:

select studno, amount, @bal := (
         case 
             when @studno = studno then @bal + amount
             else amount
         end
     ) as balance,
  @studno := studno
from
(
        select @bal := 0
             , @studno := 0
) as init,
(
select 0 as t, studno, amount, (select count(*) from tblPayables as b where a.id>b.id and a.studno=b.studno) as trN
from tblPayables as a
union all
select 1 as t, studno, -amount, (select count(*) from tblPayments as b where a.id>b.id and a.studno=b.studno) as trN
from tblPayments as a
) as q
order by studno, trN, t

http://sqlfiddle.com/#!2/9e0cf1/1

http://sqlfiddle.com/ ! 2/9e0cf1/1