PREFIX  xsd:    <http://www.w3.org/2001/XMLSchema#>
PREFIX  :       <http://example/>
PREFIX  ex:     <http://example/ns#>

# 2 Optionals, sharing a variable that is not set outside.
# Second optional introduces another variable.

SELECT *
{
   ?x :p ?z  
   OPTIONAL { ?z :q1 ?w }
   OPTIONAL { ?z :q2 ?w . ?z :q3 ?v }
}