INSERT INTO cache (reference_ID,ID,score) 

(
SELECT SQL_NO_CACHE 5 as reference_ID, 
              ID, 
                 ROUND(0 + MATCH (content) AGAINST ('здесь различные слова не более восьми')) as score 

FROM posts 
WHERE ID != '5' 
 GROUP BY ID 
 HAVING score >= 2.0  
 ORDER BY score DESC LIMIT 7
) 
  ON DUPLICATE KEY UPDATE date = NOW();

key_buffer		= 18G
sort_buffer		= 16M
myisam_sort_buffer_size = 12G
#read_buffer_size	= 1M
max_allowed_packet	= 256M
#max_join_size		= 1000000
max_sort_length		= 20
#thread_stack		= 192K
thread_cache_size       = 8
long_query_time		= 10
tmp_table_size		= 256M
max_heap_table_size	= 512M
join_buffer_size	= 224M

CREATE TABLE `posts` (
  `ID` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `date` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `title` text NOT NULL,
  `content` longtext NOT NULL,
  PRIMARY KEY (`ID`),
  KEY `date` (`date`,`ID`),
  FULLTEXT KEY `title` (`title`),
  FULLTEXT KEY `content` (`content`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8

CREATE TABLE `cache` (
  `reference_ID` bigint(20) unsigned NOT NULL DEFAULT '0',
  `ID` bigint(20) unsigned NOT NULL DEFAULT '0',
  `score` float unsigned NOT NULL DEFAULT '0',
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`reference_ID`,`ID`),
  KEY `score` (`score`),
  KEY `ID` (`ID`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8

SELECT posts.*, related.score FROM posts JOIN cache AS related ON posts.ID = related.ID WHERE related.score >= 2 AND related.reference_ID = 5 ORDER BY related.score DESC LIMIT 7

GROUP BY ID