Question

我正在尝试编写一个查询，该查询从employee_id列表中进行选择，并查找重复的图书购买（book_id）和相关的成本节省（list_price）。如果存在重复，则需要将重复book_id的数量的总和加起来。

因此，如果某人有一本与他们的employee_id相关的成本为10美元的图书，并且该图书再次提供给他们，他们就不必购买，而且可以节省10美元。如果再次发生这种情况，可以节省20美元。

我尝试过＆gt; 1但是我似乎无法正确查询查询以准确计算节省。

感谢任何帮助。

Answer 1

首先，

select employee_id, book_id, count(*)
from book_purchases
group by employee_id, book_id
having count(*) > 1

获取您需要的列表。

如果我们不必担心价格变动，那么我们只需添加一两列即可获得：

select employee_id, book_id, 
    count(*) as copies_purchased, 
    sum(list_price) as total_spent,
    count(*) - 1 as copies_unnecessarily_purchased, 
    (count(*) - 1) * avg(list_price) as amount_overspent
from book_purchases
group by employee_id, book_id
having count(*) > 1

当然，您可以加入员工并预订表格以获取名称和标题，以便稍微减少结果。

要获得每位员工超支的总金额，您可以这样包装上述查询：

select a.employee_id, sum(a.amount_overspent) as total_amount_overspent
from (
        select employee_id, book_id, 
            count(*) as copies_purchased, 
            sum(list_price) as total_spent,
            count(*) - 1 as copies_unnecessarily_purchased, 
            (count(*) - 1) * avg(list_price) as amount_overspent
        from book_purchases
        group by employee_id, book_id
        having count(*) > 1    
    ) as a 
group by a.employee_id

最后，我继续前进，加入了一张我认为你在我工作时的员工桌：

select a.employee_id, emp.employee_name, sum(a.amount_overspent) as total_amount_overspent
from (
        select employee_id, book_id, 
            count(*) as copies_purchased, 
            sum(list_price) as total_spent,
            count(*) - 1 as copies_unnecessarily_purchased, 
            (count(*) - 1) * avg(list_price) as amount_overspent
        from book_purchases
        group by employee_id, book_id
        having count(*) > 1    
    ) as a 
inner join employee as emp on emp.employee_id = a.employee_id
group by a.employee_id, emp.employee_name

要明确的是，这些不是四个单独的查询;它们只是构建您最后看到的单个查询的中间阶段。

我希望这会有所帮助。

总结重复购买

1 个答案: