如何在一个SQL查询中从几个表中计算相同的列

我有五张桌子，TDetective，TMonths，TProduct1，TProduct2和TProduct3。我想要一个包含四列的结果集：

• 首先是侦探的名字
• 第二个是计数-在特殊月份分配给这个侦探多少个TProduct1
• 第三个是计数-在特殊月份分配给这个侦探多少个TProduct2
• 第四个是计数——在特殊的月份里，有多少TProduct3分配给了这个侦探

请帮帮我

TDetective

    |id     |
    |Detective|

三个月

    |id     |
    |Months |

产品1

  |id  |
  |RequestDay|
  |Mobile|
  |Operator|
  |Subjects|
  |OccurrenceMode|
  |Detective|
  |Months|

产品2

  |id  |
  |RequestDay|
  |Mobile|
  |Operator|
  |Subjects|
  |OccurrenceMode|
  |Detective|
  |Months|

产品3

  |id  |
  |RequestDay|
  |Mobile|
  |Operator|
  |Subjects|
  |OccurrenceMode|
  |Detective|
  |Months|

我的SQL查询如下所示：

select
    TDetective.Detective,
    count(TProduct1.id) as countOfDetectiveP1
    count(TProduct2.id) as countOfDetectiveP2
    count(TProduct3.id) as countOfDetectiveP3
from
    TDetective
left outer join  
    TProduct1 on TDetective.Detective = TProduct1.Detective
where 
    TProduct1.Months in (select months from TMonths)
left outer join 
    TProduct2 on TDetective.Detective = TProduct2.Detective
where 
    TProduct2.Months in (select months from TMonths)
left outer join 
    TProduct3 on TDetective.Detective = TProduct3.Detective
where 
    TProduct3.Months in (select months from TMonths)
group by
    Detective.Detective
order by 
    Detective

---

非常感谢

我会交叉加入前两个表，以获得每个月的一行。然后使用相关子查询填写其余信息：

select d.id, d.month,
       (select count(*)
        from product1 p1
        where p1.detective = d.id and
              p1.month = m.month
       ),
       (select count(*)
        from product2 p2
        where p2.detective = d.id and
              p2.month = m.month
       ),
       (select count(*)
        from product3 p3
        where p3.detective = d.id and
              p3.month = m.month
       )
from detective d cross join
     months m;

---

您可以在外部查询中添加

where

子句，以筛选特定的侦探或月份。

将

where

替换为

和

。使用正在使用的数据库标记您的问题。

select d.Detective,
       (select count(*)
        from P118 p1
        where p1.detective = d.Detective and
              p1.Months in (select months from TempMonths)
       ),
       (select count(*)
        from P119 p2
        where p2.detective = d.Detective and
              p2.Months in (select months from TempMonths)
       ),
       (select count(*)
        from P120 p3
        where p3.detective = d.Detective and
              p3.Months in (select months from TempMonths)
       )
from Detective d 
order by Detective