mysql 多个结构相同的数据表，查询统计

        $table = "union (select keyword,count(*) as result from v9_search_tongji_2 GROUP BY keyword ORDER BY result desc )";

        $table .= "union (select keyword,count(*) as result from v9_search_tongji_3 GROUP BY keyword ORDER BY result desc )";

        $table .= "union (select keyword,count(*) as result from v9_search_tongji_4 GROUP BY keyword ORDER BY result desc )";

        $sql = " select keyword,sum(result) as u from ((select keyword,count(*) as result from v9_search_tongji GROUP BY keyword ORDER BY result desc ) ".$table.") as mmm group by mmm.keyword order by sum(result)  desc limit 10";