%META:TOPICPARENT{name="VirtTipsAndTricksGuide"}%


---+How can I use the Virtuoso specific query optimizer hint ASSUME?


<code>ASSUME</code> is a Virtuoso specific query optimizer hint for letting know the optimizer that the expression X is always true and the optimizer should work as such where you have ASSUME, while not triggering any SQL code generation for checking whether X is true (since it is ASSUMED to be true). Thus, in the example below, it is <b>ASSUMED</b> that <code>?id</code> is an IRI, so there's not need for any further type checking further down in the query-optimizer's processing workflow.

---++Usage Example:

<verbatim>
SELECT * 
WHERE 
  { 
    ?s1 <id>     ?id   ;
        geo:lat  ?lat  ;
        geo:long ?long .
    GRAPH ?rdf_view_g
      { 
        ?s2 <id>       ?id    ;
            rdfs:label ?label
      } .
    ASSUME (isIRI (?id)) } 
</verbatim>


---++Related

   * [[VirtTipsAndTricksGuide][Virtuoso Tips and Tricks Collection]]
   * [[http://docs.openlinksw.com/virtuoso/rdfsparql.html][Virtuoso Documentation]]
   * [[VirtSPARQLOptGuideEx1][Optimizing query performance using bif functions Example]]