(PECL sphinx >= 0.1.0)
SphinxClient::setGroupDistinct — Set attribute name for per-group distinct values count calculations
$attribute
   ) : bool
   Sets attribute name for per-group distinct values count calculations. Only
   available for grouping queries.  For each group, all values of
   attribute will be stored, then the amount of
   distinct values will be calculated and returned to the client. This feature
   is similar to COUNT(DISTINCT) clause in SQL.
  
attributeA string containing group-by attribute name.
   Devuelve TRUE en caso de éxito o FALSE en caso de error.