XQuery3.0 Group By Clause

gistfile1.xquery

return
  <groups> 
  {
    for $person in $persons/person
    group by 
    $country := $person/country,
    $gender := $person/@gender
    return 
      <group country="{$country}" gender="{$gender}">
        <averageAge>{avg($person/age)}</averageAge>
      </group>
  }      
  </groups>      


(:
**********************************************
   Logical result
**********************************************
Belgium             Netherlands        
Male    Female      Male        Female
---------------------------------------------
A 10    C 80        B 20        E 30
D 40                F 36        
----    ----        ----        -----
25      80          28          30

**********************************************
XQuery output:
**********************************************
<groups>
  <group country="Belgium" gender="male">
    <averageAge>25</averageAge>
  </group>
  <group country="Belgium" gender="female">
    <averageAge>80</averageAge>
  </group>
  <group country="Netherlands" gender="male">
    <averageAge>28</averageAge>
  </group>
  <group country="Netherlands" gender="female">
    <averageAge>30</averageAge>
  </group>
</groups>
:)