SELECT COUNT(link_sites.id) as count 
FROM 
       link_sites 
LEFT JOIN 
       link_query 
ON ( link_query.sender_site= 31  AND link_query.recipient_site=link_sites.id ) 
OR ( link_query.recipient_site= 31  AND link_query.sender_site=link_sites.id ) 
WHERE 
       link_sites.checked= 1  
AND link_sites.user_id<> 2  
AND link_query.sender_site 
IS NULL

ALTER TABLE `link_query` ADD INDEX ( `sender_id` ) ;
ALTER TABLE `link_query` ADD INDEX ( `recipient_site` ) ;
ALTER TABLE `link_query` ADD INDEX ( `sender_site` ) 
ALTER TABLE `link_query` ADD INDEX ( `recipient_id` ) ;

SELECT COUNT(link_sites.id) as count 
FROM 

       link_sites 
LEFT JOIN 
        link_query as link_query_se
        ON ( link_query_se.sender_site= 31  AND link_query_se.recipient_site=link_sites.id ) 
LEFT JOIN 
        link_query  as link_query_re
        on
        ( link_query_re.recipient_site= 31  AND link_query_re.sender_site=link_sites.id ) 

WHERE 
       link_sites.checked= 1  
 AND link_sites.user_id!= 2  
 AND 
 (
 link_query_se.sender_site IS NULL
 and
 link_query_re.sender_site IS NULL)