sparql - SPARQL 查询中的两个选择的联合

Question

我想做类似的事情

{
    SELECT ?page, "A" AS ?type WHERE 
    {
         ?s rdfs:label "Microsoft"@en;
            foaf:page ?page
    }
}
UNION
{
    SELECT ?page, "B" AS ?type WHERE 
    {
         ?s rdfs:label "Apple"@en;
            foaf:page ?page
    }
}

但这会产生语法错误。如何在 SPARQL 中合并两个选择查询？

Answer 1

你可以像这样联合它们：

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT * WHERE
{ 
{
    SELECT ?page ("A" AS ?type) WHERE 
    {
         ?s rdfs:label "Microsoft"@en;
            foaf:page ?page
    }
}
UNION
{
    SELECT ?page ("B" AS ?type) WHERE 
    {
         ?s rdfs:label "Apple"@en;
            foaf:page ?page
    }
}
}

（检查SPARQL 验证器）

但是，对于这种情况，我认为您根本不需要子查询。例如：

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?page ?type WHERE
{
    ?s foaf:page ?page .
    { ?s rdfs:label "Microsoft"@en . BIND ("A" as ?type) }
    UNION
    { ?s rdfs:label "Apple"@en . BIND ("B" as ?type) }
}

Answer 2

根据@user205512 的回答，这是适用于 Virtuoso 的答案：

SELECT * {
    ?s foaf:page ?page .
    {
        SELECT ?page ("A" AS ?type) {
            ?s rdfs:label "Microsoft"@en;
               foaf:page ?page
        }
    } UNION {
        SELECT ?page ("B" AS ?type) {
            ?s rdfs:label "Apple"@en;
               foaf:page ?page
        }
    }
}

诀窍就是?s foaf:page ?page在UNION. 这显然是多余的，但它似乎避免了 Virtuoso 错误，这显然是当你有一个“裸”UNION的子查询时引起的。