RDFlib 计数在 SPARQL 查询中不起作用

Question

我正在使用本机商店（Sleepycat）探索基于 python 的库“RDFlib”。 基本的“select * ...”查询工作正常，但 COUNT 似乎不起作用。
这是我的代码：

from rdflib import ConjunctiveGraph, Namespace, Literal 
path = './mytriplestore'
graph = ConjunctiveGraph('Sleepycat')
graph.open(path, create = False)
query = """SELECT count(?o)
   WHERE {
     <http://examplesubject> ?p ?o.
   }
   Limit 10"""

qres = graph.query(query)
for row in qres:
   print row

错误：

File "/usr/local/lib/python2.7/dist-packages/rdflib/graph.py", line 1085, in query
query_object, initBindings, initNs, **kwargs))
File "/usr/local/lib/python2.7/dist-packages/rdflib/plugins/sparql/processor.py", line 74, in query
parsetree = parseQuery(strOrQuery)
File "/usr/local/lib/python2.7/dist-packages/rdflib/plugins/sparql/parser.py", line 1058, in parseQuery
return Query.parseString(q, parseAll=True)
File "/usr/local/lib/python2.7/dist-packages/pyparsing-1.5.7-py2.7.egg/pyparsing.py", line 1006, in parseString
raise exc
pyparsing.ParseException: Expected "?" (at char 7), (line:1, col:8)

谁能帮我解决这个问题？

Answer 1

您必须使用 group by 才能获得计数结果，请尝试以下操作：

query = """SELECT count(?o) As ?count
   WHERE {
     <http://examplesubject> ?p ?o.
   }
   GROUP BY ?o
   Limit 10"""