Все проще есть же replace() if($tematic = (int)$this->getProperty('tematic')){
$query->innerJoin('modTemplateVarResource',
'tematic', "tematic.contentid = {$this->classKey}.id AND
tematic.tmplvarid = 14 AND find_in_set('{$tematic}', replace(tematic.value, '||', ',') )");
}