SELECT DISTINCT UPPER(LEFT(contact_a.sort_name, 1)) as sort_name  
FROM civicrm_contact contact_a  
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-101` 
    ON contact_a.id = `civicrm_group_contact-101`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-102` 
    ON contact_a.id = `civicrm_group_contact-102`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-46` 
    ON contact_a.id = `civicrm_group_contact-46`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-60` 
    ON contact_a.id = `civicrm_group_contact-60`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-6` 
    ON contact_a.id = `civicrm_group_contact-6`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-94` 
   ON contact_a.id = `civicrm_group_contact-94`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-95` 
    ON contact_a.id = `civicrm_group_contact-95`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-97` 
    ON contact_a.id = `civicrm_group_contact-97`.contact_id    
  LEFT JOIN civicrm_group_contact `civicrm_group_contact-99` 
    ON contact_a.id = `civicrm_group_contact-99`.contact_id    
  LEFT JOIN civicrm_group_contact_cache `civicrm_group_contact_cache_6` 
    ON contact_a.id = `civicrm_group_contact_cache_6`.contact_id   
WHERE  
  ( 
   ( 
    ( `civicrm_group_contact-6`.group_id IN ( 6 ) 
     AND 
      `civicrm_group_contact-6`.status IN ("Added" ) 
     ) 
     OR 
     ( `civicrm_group_contact_cache_6`.group_id = 6 
     ) 
    )
   )  
   AND  
   (  
    ( `civicrm_group_contact-6`.group_id IN ( 6 ) 
    AND `civicrm_group_contact-6`.status IN ("Added")
   )  
   OR  
   ( `civicrm_group_contact-46`.group_id IN ( 46 ) 
   AND `civicrm_group_contact-46`.status IN ("Added") 
   )  
  OR  
   ( `civicrm_group_contact-60`.group_id IN ( 60 ) 
   AND `civicrm_group_contact-60`.status IN ("Added") 
  ) OR ( `civicrm_group_contact-94`.group_id IN ( 94 ) 
  AND `civicrm_group_contact-94`.status IN ("Added") )  
  OR  ( `civicrm_group_contact-95`.group_id IN ( 95 ) 
  AND `civicrm_group_contact-95`.status IN ("Added") )  
  OR  ( `civicrm_group_contact-97`.group_id IN ( 97 ) 
  AND `civicrm_group_contact-97`.status IN ("Added") )  
  OR  ( `civicrm_group_contact-99`.group_id IN ( 99 ) 
  AND `civicrm_group_contact-99`.status IN ("Added") )   
  OR  ( `civicrm_group_contact-101`.group_id IN ( 101 ) 
  AND `civicrm_group_contact-101`.status IN ("Added") )  
  OR  ( `civicrm_group_contact-102`.group_id IN ( 102 ) 
  AND `civicrm_group_contact-102`.status IN ("Added") )  );

Was sich die Entwickler dabei dachten ist mir nicht klar, denn es ist nichts anderes als

SELECT DISTINCT UPPER(LEFT(contact_a.sort_name, 1)) as sort_name  
FROM civicrm_contact contact_a;

Sprich die Menge aller Großbuchstaben des ersten Buchstaben von sort_name.

*kopfkratz*

Danke an Rince der mit der Query in #mysql.de aufschlug.
Wer Lust hat ist gerne eingeladen auch im irc aufzuschlagen:)