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

---+ Are custom SPARQL extension functions supported?  How can I use them?

Virtuoso supports two ways to write one's own custom [[http://www.w3.org/TR/rdf-sparql-query/#extensionFunctions][SPARQL extension functions]]: 

%TOC%

---++ Use a Stored Procedure

You can create a SQL stored procedure in Virtuoso PL and, call it using the <code><b>sql:</b></code> prefix:
<verbatim>
SQL> CREATE PROCEDURE testfunc()
  {
    -- your code here
  }
;

Done;

SQL> SPARQL 
SELECT * 
  WHERE
    { 
      ?s  ?p  `sql:testfunc(?o)` 
    };
</verbatim>

For more details see [[http://docs.openlinksw.com/virtuoso/rdfsparql.html#rdfsqlfromsparql][Calling SQL from SPARQL]] Virtuoso Documentation.

---++  Create a built-in function

You can also make a built-in function, which is basically a <code>C</code> function that can be called from both SQL and SPARQL, as in the  
example from below, using the <code><b>bif:</b></code> prefix.

In this SPARQL example, we use the <code>CONTAINS</code> function to do a freetext search on all <code>?o</code> that contain words starting with <code>"Timo"</code>.

<verbatim>
SELECT * 
  FROM <http://www.w3.org/people#> 
  WHERE 
    { 
      ?s  ?p            ?o         . 
      ?o  bif:contains  '"Timo*"'
    }
</verbatim>


For more details see [[http://docs.openlinksw.com/virtuoso/sparqlextensions.html#rdfsparqlrulefulltext][Using Full Text Search in SPARQL]] Virtuoso Documentation.

This feature also allows you to use relevant functions from the [[http://docs.openlinksw.com/virtuoso/functions.html][Virtuoso SQL Functions Guide]] inside a SPARQL query.


---++ Related
   
   * [[VirtTipsAndTricksGuide][Virtuoso Tips and Tricks Collection]]
   * [[http://docs.openlinksw.com/virtuoso/sparqlextensions.html][Virtuoso Documentation]]