[英]GROUP BY in SPARQL?
Assume that I uses the FOAF ontology. 假设我使用FOAF本体。 I want to return the name
and the mbox
for each person. 我想为每个人返回name
和mbox
。 I use the following query: 我使用以下查询:
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT DISTINCT ?name ?email
WHERE {
?person foaf:name ?name.
?person foaf:mbox ?email.
}
The result of the join is a set of rows: ?person
, ?name
, ?email
. 连接的结果是一组行: ?person
, ?name
, ?email
。 This query is returning the ?name
and ?email
. 此查询返回?name
和?email
。 Note that in some of the ?person
may have multiple mailboxes, so in the returned set, a ?name
row may appear multiple times, once for each mailbox. 请注意,在某些?person
可能有多个邮箱,因此在返回的集中, ?name
行可能会多次出现,每个邮箱一次。
Is there a solution to make a GROUP BY person ?name
? 是否有解决方案来制作GROUP BY person ?name
?
You can group by person but then you need an aggregation for ?name
and ?email
您可以按人分组,但是您需要聚合?name
和?email
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT (sample(?name) AS ?name2) (sample(?email) as ?email2)
WHERE {
?person foaf:name ?name.
?person foaf:mbox ?email.
} GROUP BY ?person
SAMPLE
picks one possible from the group for each ?person
. SAMPLE
为每个?person
选择一个可能的组。
or maybe 或者可能
SELECT (group_concat(?name) AS ?names)
(except that's a string). (除了那是一个字符串)。
It may be easier work with 它可能更容易使用
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?name ?email
WHERE {
?person foaf:name ?name.
?person foaf:mbox ?email.
}
ORDER BY ?person ?name ?email
and process the results in your application where you know the incoming results have all the entries for one person is a single section of the results. 并在您的应用程序中处理结果,您知道传入的结果包含一个人的所有条目是结果的单个部分。
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