运行减法，但仅在金额仍高于限制时减法

Question

我有一个具有以下结构的 table，我想将 TotalAmount 减去 Amount，但前提是剩余金额仍高于限制。排序是在继续下一个数据之前应该首先尝试的顺序

Sort    Amount    Limit    TotalAmount
1       200       500      2000
3       500       500      2000
10      1000      500      2000
17      30        500      2000

预期结果

Sort    Amount    Limit    TotalAmount    RemainingAmount
1       200       500      2000           1800
3       500       500      2000           1300  
10      1000      500      2000           1300  --This is still 1300 because 1300 - 1000 is 300
17      30        500      2000           1270

我一直在尝试 window 函数，但我不知道如何应用在条件下保持相同数量的逻辑。

SELECT Sort, Amount, Limit, TotalAmount, TotalAmount - SUM(Amount) OVER (ORDER BY Sort) as RemainingAmount

我也尝试了一些案例并检查我是否低于限制

CASE WHEN TotalAmount - SUM(Amount) OVER (ORDER BY Sort) < Limit THEN --readd the amount again?

Answer 1

您可以执行自我 join 生成基线运行总计，然后找到每个给定 sort 的最小运行总计，当减去sort 的金额不低于限制：

with aggs(s, a) as (
   select v.sort, sum(coalesce(v1.amount, 0)) from vals v 
   left join vals v1 on v1.sort < v.sort 
   group by v.sort order by v.sort
),
r_m(s, a) as (
   select v.sort, min(v.totalamount - a1.a) from vals v 
   join aggs a1 on v.totalamount - a1.a >= v.lmt and v.sort >= a1.s
   group by v.sort
   order by v.sort
)
select v.*, case when r_m.a - v.amount >= v.lmt 
                 then r_m.a - v.amount else r_m.a end 
from vals v join r_m on v.sort = r_m.s

输出：

sort	amount	lmt	totalamount	remainingamount
1	200	500	2000	1800
3	500	500	2000	1300
10	1000	500	2000	1300
17	30	500	2000	1270

Answer 2

声明一个运行变量 @Amount 以记住扣除的金额并对所选的每一行进行计算。

SELECT Sort, Amount, `Limit`, TotalAmount, 
CASE WHEN TotalAmount - @Amount - Amount < `Limit` 
     THEN TotalAmount - @Amount ELSE TotalAmount - (@Amount := @Amount + Amount) 
     END AS RemainingAmount
FROM v 
JOIN ( SELECT @Amount := 0 ) f
ORDER BY Sort

运行减法，但仅在金额仍高于限制时减法

Running subtraction but subtracting only if the amount is still above a limit

mysql

sql

mysql-8.0

运行 减法，但仅在金额仍高于限制时减法

Running subtraction but subtracting only if the amount is still above a limit

mysql

sql

mysql-8.0

运行减法，但仅在金额仍高于限制时减法