sql - oracle sql left join 和 count, sum, group by

Question

我想计算每个问题的项目数量、金额和总百分比，仅限于给定的资助者和财政年度。出于某种原因，当我运行下面的查询时，我没有看到 null来自左联接的值。

项目和问题的关系是一个问题可以有很多项目。问题表由目标表链接。

已更新

select 
   q.sp_question_id,
   count(p.project_id) as projectCount,
   sum(p.funding) as amount,
   round(sum(p.funding)/sum(sum(p.funding)) over() *100) as percentTotal 
from questions q 
   left join projects p on p.fiscal_year = q.fiscal_year  
   join objectives o on o.sp_objective_id = p.sp_objective_id 
     and o.sp_question_id = q.sp_question_id 
     and o.fiscal_year = p.fiscal_year 
     and o.fiscal_year = 2014  
   join funders f on p.funder_id = f.funder_id 
where f.funder_short_name ='foo' 
   and q.fiscal_year = 2014  
group by q.sp_question_id 
order by q.sp_question_id;

---

 questionId   projectCount  amount          percentTotal
 q1           14            54510           4
 q2           29            1083598.72      76
 q3           1             19900           1
 q4           5             145631          10
 q5           1             124999          9
 q6           1             0               0 

---

预期结果

 questionId   projectCount  amount          percentTotal
 q1           14            54510           4
 q2           29            1083598.72      76
 q3           1             19900           1
 q4           5             145631          10
 q5           1             124999          9
 q6           1             0               0
 q7       <null>            <null>          <null>

---

一直向下查询左连接

select 
       q.sp_question_id,
       count(p.project_id) as projectCount,
       sum(p.funding) as amount,
       round(sum(p.funding)/sum(sum(p.funding)) over() *100) as percentTotal 
    from questions q 
       left join projects p on p.fiscal_year = q.fiscal_year  
       left join objectives o on o.sp_objective_id = p.sp_objective_id 
         and o.sp_question_id = q.sp_question_id 
         and o.fiscal_year = p.fiscal_year 
         and o.fiscal_year = 2014  
       left join funders f on p.funder_id = f.funder_id 
    where f.funder_short_name ='foo' 
       and q.fiscal_year = 2014  
    group by q.sp_question_id 
    order by q.sp_question_id;

---

结果

 questionId   projectCount  amount          percentTotal
 na           51            1428638.72      11
 q1           51            1428638.72      11
 q2           51            1428638.72      11
 q3           51            1428638.72      11
 q4           51            1428638.72      11
 q5           51            1428638.72      11
 q6           51            1428638.72      11
 q7           51            1428638.72      11
 qother       51            1428638.72      11

---

一直向下查询左连接并调整 where 子句

select 
   q.sp_question_id,
   count(p.project_id) as projectCount,
   sum(p.funding) as amount,
   round(sum(p.funding)/sum(sum(p.funding)) over() *100) as percentTotal 
from questions q 
   left join projects p on p.fiscal_year = q.fiscal_year 
   left join objectives o on o.sp_objective_id = p.sp_objective_id 
     and o.sp_question_id = q.sp_question_id 
     and o.fiscal_year = p.fiscal_year and o.fiscal_year = 2014 
   left join funders f on p.funder_id = f.funder_id and f.funder_short_name ='foo' 
   where q.fiscal_year = 2014 
group by q.sp_question_id 
order by q.sp_question_id;

---

结果

 questionId   projectCount  amount          percentTotal
 na           1225          299628985.01    11
 q1           1225          299628985.01    11
 q2           1225          299628985.01    11
 q3           1225          299628985.01    11
 q4           1225          299628985.01    11
 q5           1225          299628985.01    11
 q6           1225          299628985.01    11
 q7           1225          299628985.01    11
 qother       1225          299628985.01    11

Answer 1

您遇到的问题与 sql 中最不为人知的问题之一有关:关系的传递性。

您在项目和问题之间进行可选(外部)连接，但您要求在项目和目标(和资助者)之间建立强制(内部连接)关系:

计算中间结果集的传递系统使内连接占优势，这基本上意味着中间的外连接被忽略了。准确的说，它并没有被忽略，而是变成了一个inner join。

您得到的是内部联接一直向下的结果，而您实际上期望左联接按原样运行并为与任何项目无关的问题返回空行...但是引擎确实如此不像上面描述的那样工作。

在我的头脑中，我只是认为你可以一直使用左连接。但是您可能会遇到比预期更多的空行。这实际上取决于您对数据的处理方式。

此外，您的查询中似乎有一个应该修改的广泛连接。请试试这个:

select 
   q.sp_question_id,
   count(p.project_id) as projectCount,
   sum(p.funding) as amount,
   round(sum(p.funding)/sum(sum(p.funding)) over() *100) as percentTotal 
from questions q 
   left join objectives o on 
         o.sp_question_id = q.sp_question_id 
     and o.fiscal_year = 2014 
   left join projects p on o.fiscal_year = p.fiscal_year and o.sp_objective_id = p.sp_objective_id 
   left join funders f on p.funder_id = f.funder_id and f.funder_short_name ='foo' 
where q.fiscal_year = 2014 
group by q.sp_question_id 
order by q.sp_question_id;