表连接列

Question

我执行的查询似乎忽略了子查询中的where子句 （从b.amazon = 2和manifest = a.dbid的订单中选择计数（亚马逊）

列亚马逊是INT类型 SQL SERVER 2014

如果我自己运行查询并输入清单值，我会得到正确的结果，我期待并且是1

从亚马逊= 2和清单=＆＃39; 211104＆＃39;的订单中选择计数（亚马逊） 结果返回1

当我运行下面的查询时，我得到的结果为5，即清单= 211104的所有订单的计数，但亚马逊的值在4个结果中为1，结果为2个。

Select  distinct
top 30 DBID, today ,sum([amazon-orders])
From
(
    SELECT [dbid], [today], 
        (select count(amazon) from orders 
         where b.amazon = 2 and manifest = a.dbid) as [amazon-orders]
    FROM [manifest] a
    join orders b on a.[dbid] = b.[manifest]
) t1  
Group By 
DBID, today
order by dbid desc

有人可以帮帮我吗。

由于

Answer 1

你有一个额外的连接，所以你多次计数......这样做：

Select  distinct
top 30 DBID, today ,sum([amazon-orders])
From
(
    SELECT [dbid], [today], 
        (select count(amazon) from orders b
         where b.amazon = 2 and manifest = a.dbid) as [amazon-orders]
    FROM [manifest] a
) t1  
Group By 
DBID, today
order by dbid desc

或者像这样

SELECT [dbid], [today], count(o.amazon)
FROM [manifest] a
join orders o on a.dbid = o.manifest and o.amazon = 2
group by dbid, today

或者如果你有不想加入的列（在你的查询中只有这一个连接，你需要使用左连接）：

SELECT [dbid], [today], sum(case when o.amazon is not null then 1 else 0 end)
FROM [manifest] a
left join orders o on a.dbid = o.manifest and o.amazon = 2
group by dbid, today

Answer 2

这是怎么回事？

SELECT top 30 [dbid], [today], sum(case when b.amazon = 2 then 1 else 0 end) as [amazon-orders]
FROM [manifest] a
join orders b on a.[dbid] = b.[manifest]
group by DBID, today
order by dbid desc

非常确定，因为您的查询实际上连接了两次订单，所以增加了计数。

Answer 3

使用此：

select  a.DBID, a.today, count(b.amazon) from [manifest] a
join orders b on a.[dbid] = b.[manifest] and b.amazon = 2
Group By a.DBID, a.today