SPARQL分组依据和排序依据:未排序 [英] SPARQL group by and order by: not ordered

问题描述

我会跟踪查询其中schema.org数据库用于查找类的子级数-作为比我的应用程序更简单的数据库.我想获得按字母顺序连接的孩子的名字.查询:

I follow up on query where the schema.org database is used to find the number of children of a class - as a simpler database than my application. I want to get the names of the children concatenated in alphabetic order. The query:

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

select    ?child  (group_concat (?string) as ?strings) 
where {
  ?child  rdfs:subClassOf schema:Event .
     ?grandchild rdfs:subClassOf ?child .
  bind (strafter(str(?grandchild), "http://schema.org/") as ?string)
}   group by ?child  order by asc(?string)
limit 20 

给予

schema:PublicationEvent   "OnDemandEvent BroadcastEvent"
schema:UserInteraction    "UserPageVisits UserComments UserPlays UserBlocks UserDownloads UserPlusOnes UserLikes UserCheckins UserTweets"

哪个不是按字母顺序排列的.如果将排序顺序替换为desc，则结果完全相同.我似乎不明白group by，order by和可能的bind是如何相互作用的.

Which is not alphabetically ordered. If I replace the sort order to desc the result is exactly the same. I seem not to understand how group by, order by and possibly bind interact.

推荐答案

还需要一个附加的select子查询才能将顺序推入组中

An additional select subquery is required to push the order inside the groups:

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

select    ?child  (group_concat (?string) as ?strings) 

where {
    select * 
    {
     ?child  rdfs:subClassOf schema:Event .
     ?grandchild rdfs:subClassOf ?child .
     bind (strafter(str(?grandchild), "http://schema.org/") as ?string)
    } order by asc(?string)
}   group by ?child  
limit 20 

这篇关于SPARQL分组依据和排序依据:未排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！