Question

我需要帮助从sql中获得某些结果 用户表：

userid | name
-------|-----------
1      | Bob Robert
2      | Steve Smith
3      | Willard Henegar
4      | Max Rockwell
5      | Marion Paley
6      | Marcus Delisle

订单表：

orderid | userid
--------|-------
1       |1
2       |1
3       |1
4       |2
5       |3
6       |2
7       |4
8       |4
9       |5
10      |4
11      |4
12      |1

想要的结果

numOrders | numPeople
----------|----------
0         |1
1         |2
2         |1
3         |0
4         |2

所以基本上我想表明有多少人没有订单，有多少人有1个订单，2个订单等
我试图搞清楚并想出了这个：

SELECT
 Count(orders.orderid) AS numOrders,
 Count(users.userid)   AS numPeople 
FROM   users 
       LEFT JOIN orders 
              ON users.userid = orders.userid 
GROUP  BY numOrders

但这给了我一个错误，我无法对numOrders进行分组。

关于如何实现这一目标的任何建议？

Answer 1

你想要一个双直方图。这是最简单的方法：

select cnt, count(*), min(userid), max(userid)
from (select u.userid, count(o.userid) as cnt
      from users u left join
           orders o
           on u.userid = o.userid
      group by u.userid
     ) u
group by cnt;

但是，这不会为您提供0计数的行。这需要更多的努力。如果您有一个numbers表来填补缺失的值，这会有所帮助。

Answer 2

select count(userid), numorders 
from(
SELECT
Count(*) AS numOrders,
userid 
from orders 
group by userid ) t
group by numorders

Orders表就足够了，因为您只需要订单和用户数。

Answer 3

如果您还希望用户没有任何订单，您可以执行以下操作：

select NumOrders, count(*) as NumPeople
from (
    select u.UserId, count(*) as NumOrders
    from users u
    left join orders o on o.UserId = o.UserId
group by o.UserId
) t
group by t.NumOrders

你也可以这样做：

select NumOrders, count(*) as NumPeople
from (
    select
    u.UserId, 
    (select count(*) from orders o where o.UserId = u.UserId) as NumOrders
from users u
) t
group by t.NumOrders

戈登提到，拥有一张数字表会有所帮助。如果你知道没有人会说超过1000个订单，并且你想要为每个0到1000的数字显示一行，你可以这样做：

select number as NumPeople, isnull(p.NumOrders, 0) as NumOrders
from master..spt_values v
left join 
(
    select t.NumOrders, count(*) as NumPeople
    from ( select
            u.UserId, 
            (select count(*) from order o where o.UserId = u.UserId) as NumOrders
    from users u) t
    group by NumOrders
) p on p.NumOrders = v.number
where type = 'P'
and number <= 1000

以上内容适用于SQL Server。我不确定MySQL是否有主值表，否则，您可以轻松创建一个数字表并将其交换出来。

SQL计数按订单数量计算的人数

3 个答案: