选择 sum 直到设定数量,然后更新 mysql 数据库中的字段 [英] Select sum until a set amount and then update fields in mysql database
问题描述
item_id rate status
--------- ----------- ------
1 12 credit
2 10 credit
3 10 credit
4 20 cash
5 55 credit
我有上面的表格,一个用户输入和 25 的金额.现在我想更新具有信用作为状态的行的状态,从信用到现金,直到利率总和为 25,所以在上表中总和为 22 的 1 行应获得现金状态.由于用户输入是 25,我仍然有 3 的余额(25-22),这个余额应该从第三行中扣除,使第三行的比率为 7.我想要的结果是表格形式,其中突出显示了更改:>
I have the above table, A user inputs and amount of 25. Now I want to update the status of the rows having credit as status from credit to cash until the sum of rate is 25, so in the above table the top 1 rows having a sum of 22 should get a status of cash. Since the user input is 25, I still have a balance of 3 (25-22), this balance should be deducted from the third row making the third row rate 7. The result I want is tabular form with the changes highlighted:
item_id rate status
--------- ----------- ------
1 12 **cash**
2 10 **cash**
3 **7** credit
4 20 cash
5 55 credit
推荐答案
您可以使用窗口函数来识别需要更改的行:
You can use window functions to identify the rows that need to be changed:
select item_id,
case when sum_rate >= 25 then 'credit' else 'cash' end as status,
case when sum_rate >= 25 then sum_rate - 25 else rate end as rate
from (
select t.*, sum(rate) over(order by item_id) sum_rate
from mytable t
where status = 'credit'
) t
where sum_rate - rate < 25
如果您愿意,可以将该逻辑放在 update
语句中:
You can put that logic in an update
statement if you prefer:
update mytable t
inner join (
select item_id, sum(rate) over(order by item_id) sum_rate
from mytable t
where status = 'credit'
) t1 on t1.item_id = t.item_id
set
t.status = case when sum_rate >= 25 then 'credit' else 'cash' end,
t.rate = case when t1.sum_rate >= 25 then t1.sum_rate - 25 else t.rate end
where t1.sum_rate - t.rate < 25
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