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%META:TOPICPARENT{name="VirtTipsAndTricksGuide"}% ---++What is the difference between the functions SAMPLE, <nowiki>GROUP_CONCAT</nowiki> and <nowiki>GROUP_DIGEST</nowiki>? This example demonstrates the differences between the functions <code>[[http://docs.openlinksw.com/virtuoso/fn_SAMPLE.html][SAMPLE]]</code>, <code>[[http://docs.openlinksw.com/virtuoso/fn_GROUP_CONCAT.html][<nowiki>GROUP_CONCAT</nowiki>]]</code> and <code>[[http://docs.openlinksw.com/virtuoso/fn_GROUP_DIGEST.html][<nowiki>GROUP_DIGEST</nowiki>]]</code>. Assume the following query that should get all <code>?assets</code> as a list with delimiters: <verbatim> SPARQL SELECT ?view ?path (sql:GROUP_CONCAT (?asset, ' ')) as ?asset_list FROM <http://mygraph.com> WHERE { ?view <viewPath> ?path ; <viewContent> ?asset ; <viewType> 'phyview'. } ; </verbatim> This method is not universal, because conversion to strings will eliminate the difference between strings and IRIs and there should be some delimiter that never appears in values of <code>?asset</code>. In addition, the query may fail with "row too long" error if values of <code>?asset</code> are lengthy and/or numerous enough. It is also possible the query not work completely free from duplicates if more than one list is desired. E.g.: <verbatim> SPARQL SELECT ?view (sql:GROUP_CONCAT (?path, ' ')) as ?path_list (sql:GROUP_CONCAT (?asset, ' ')) as ?asset_list FROM <http://mygraph.com> WHERE { ?view <viewPath> ?path ; <viewContent> ?asset ; <viewType> 'phyview' . } </verbatim> will not contain duplicates in lists only if either <code>?path</code> or <code>?asset</code> is unique for every found <code>?view</code>; but if it's so unique then there's no need in the corresponding <code>sql:[[http://docs.openlinksw.com/virtuoso/fn_GROUP_CONCAT.html][<nowiki>GROUP_CONCAT</nowiki>]]()</code> . If there are many values per property but it's enough to return any single value and ignore the rest then use <code>sql:[[http://docs.openlinksw.com/virtuoso/fn_SAMPLE.html][SAMPLE]]()</code> function instead of <code>sql:[[http://docs.openlinksw.com/virtuoso/fn_GROUP_CONCAT.html][<nowiki>GROUP_CONCAT</nowiki>]]() </code>. If there are many values per property and it's better to show more than one value but "row too long" error happens, then the <code>sql:[[http://docs.openlinksw.com/virtuoso/fn_GROUP_DIGEST.html][<nowiki>GROUP_DIGEST</nowiki>]]</code> function can be used: <verbatim> SPARQL SELECT ?view (sql:GROUP_DIGEST (?path, ' ', 1000, 1)) as ?path_list (sql:GROUP_DIGEST (?asset, ' ', 1000, 1)) as ?asset_list FROM <http://mygraph.com> WHERE { ?view <viewPath> ?path ; <viewContent> ?asset ; <viewType> 'phyview' . } </verbatim> ---++Related * [[VirtTipsAndTricksGuide][Virtuoso Tips and Tricks Collection]] * [[http://docs.openlinksw.com/virtuoso/fn_SAMPLE.html][SAMPLE]] * [[http://docs.openlinksw.com/virtuoso/fn_GROUP_CONCAT.html][<nowiki>GROUP_CONCAT</nowiki>]] * [[http://docs.openlinksw.com/virtuoso/fn_GROUP_DIGEST.html][<nowiki>GROUP_DIGEST</nowiki>]]

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