如何通过查询获得 sparql 组中的总计

Question

我跟进 query，其中 schema.org 数据库用于查找 class 的 children 的数量。每个 class 的答案给出了 children 的数量。在我的应用程序中，我需要所有 children 的总计（即每个组的计数总和），以便为每个组计算 children 总数的百分比。我从上一个问题得到的查询是：

prefix schema:  <http://schema.org/>
prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#>

select   ?child (count(?grandchild) as ?nGrandchildren) 
from <http://localhost:3030/testDB/data/schemaOrg>
where {
  ?child rdfs:subClassOf schema:Event .
  optional { 
    ?grandchild rdfs:subClassOf ?child
  }
}  group by ?child

给出了预期的答案（children 的事件和数量）。如何得到总数？我尝试了一个嵌套查询：

prefix schema:  <http://schema.org/>
prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#>

select   ?child (count(?grandchild) as ?nGrandchildren) 
from <http://localhost:3030/testDB/data/schemaOrg>
where {
  select (count(?grandchild) as ?grandTotal) 
  {?child rdfs:subClassOf schema:Event .
  optional { 
    ?grandchild rdfs:subClassOf ?child
     }
   }
}  group by ?child

但得到一个答案：“”-> 0。

Answer 1

此查询使用两个 sub-SELECTs： * 第一个计算每个 child 的 grandchildren 数 * 第二个returns总人数grandchildren

prefix schema:  <http://schema.org/>
prefix rdfs:    <http://www.w3.org/2000/01/rdf-schema#>

select ?child ?nGrandchildren 
(round(?nGrandchildren/?totalGrandchildren * 100) as ?percentageGrandchildren) {

# compute number per child
{
select ?child (count(?grandchild) as ?nGrandchildren) where {
  ?child rdfs:subClassOf schema:Event .
  optional { 
    ?grandchild rdfs:subClassOf ?child
  }
}
group by ?child
}

# compute total number
{
select (count(?grandchild) as ?totalGrandchildren) where {
  ?child rdfs:subClassOf schema:Event .
  optional { 
    ?grandchild rdfs:subClassOf ?child
  }
}
}

}

输出

-----------------------------------------------------------------------------------------------
| child                   | nGrandchildren | percentageGrandchildren                          |
===============================================================================================
| schema:UserInteraction  | 9              | "82"^^<http://www.w3.org/2001/XMLSchema#decimal> |
| schema:FoodEvent        | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:MusicEvent       | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:PublicationEvent | 2              | "18"^^<http://www.w3.org/2001/XMLSchema#decimal> |
| schema:LiteraryEvent    | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:SportsEvent      | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:DanceEvent       | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:ScreeningEvent   | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:DeliveryEvent    | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:ExhibitionEvent  | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:EducationEvent   | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:SaleEvent        | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:VisualArtsEvent  | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:CourseInstance   | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:ChildrensEvent   | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:BusinessEvent    | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:Festival         | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:ComedyEvent      | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:TheaterEvent     | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
| schema:SocialEvent      | 0              | "0"^^<http://www.w3.org/2001/XMLSchema#decimal>  |
-----------------------------------------------------------------------------------------------

如何通过查询获得 sparql 组中的总计

How to get grand total in a sparql group by query

sparql

输出