Question

我有两个postgress表Users（用户标识，城市，电子邮件）和Purchase（用户标识，商品标识，名称，金额），我想运行一个查询，以便向我提供一个用户标识购买的商品总数，并向我提供总额由用户花费。如何获得这些结果？

Answer 1

您需要使用count()，sum()函数和group by。试试：

select u.userID, count(p.ItemID) as TotalItemsPurchased, sum(p.amount) as TotalAmountSpent
from Users u
inner join Purchase p on p.userID = u.userID
group by u.userID

Answer 2

select couserID, count(p.ItemID) as "TotalItemsPurchased", sum(p.amount) as "TotalAmountSpent" from Users u 
inner join Purchase p on p.userId = u.userId
group by userID

Answer 3

如果您只关心购物的用户，则不需要join：

select p.user_id, count(*), sum(p.amount)
from purchases p
group by p.user_id;

如果您也关心没有购物的用户，请使用left join：

select u.user_id, count(p.user_id), sum(p.amount)
from users u left join
     purchases p
     on u.user_id = p.user_id
group by u.user_id;

在分组的列中添加值

3 个答案: