The firm owns several buy-back centers for collection of recyclable materials. Each of them receives funds to be paid to the recyclables suppliers. Data on funds received is recorded in the table
Income_o(point, date, inc)
The primary key is (point, date), where point holds the identifier of the buy-back center, and date corresponds to the calendar date the funds were received. The date column doesn’t include the time part, thus, money (inc) arrives no more than once a day for each center. Information on payments to the recyclables suppliers is held in the table
Outcome_o(point, date, out)
In this table, the primary key (point, date) ensures each buy-back center reports about payments (out) no more than once a day, too.
For the case income and expenditure may occur more than once a day, another database schema with tables having a primary key consisting of the single column code is used:
Income(code, point, date, inc)
Outcome(code, point, date, out)
Here, the date column doesn’t include the time part, either.
Under the assumption that receipts of money (inc) and payouts (out) can be registered any number of times a day for each collection point [i.e. the code column is the primary key], display a table with one corresponding row for each operating date of each collection point.
Result set: point, date, total payout per day (out), total money intake per day (inc).
Missing values are considered to be NULL.
(最后一句不是报错，是题目要求，我没有想到合适的解决方案，故没有贴出SQL代码)
sql语句应当贴出来，这样只有错误从何分析？
Missing values are considered to be NULL. 缺少的值被认为是空值。
楼上正解~Missing values are considered to be NULL. 缺少的值被认为是空值。
缺少的值被认为是空值
感觉你没有赋值的字段，默认为NULL值了，显式赋值试试
你的字段里存在有NULL值。。。在求和时出错，，最好把sql语句贴出来
是的，最好把sql贴出来，只看报错不好定位的
没有sql，感觉和“巧妇难为无米之炊”一样
赋值的时候出现空值。最好把sql贴出来看一下
报空值错误，把sql贴出来，才能更好的帮助到您
谢谢各位，但是Missing values are considered to be NULL.并不是报错，而是题目的要求，这道题本身我没有想到合适的解决方案。
单从报错角度来看应该是赋值空了，但是没有具体的sql看不出具体的问题
不给sql语句就罢了，至少给出如何重现问题的步骤啊。