求助sql语句，没分了，唉……

在mysql下,谁能帮我把这个sql语句优化一下，谢谢了



SELECT *
FROM (

SELECT `country_name` , count( * ) AS num
FROM `lomo_track_201106`
GROUP BY `country_name`
ORDER BY num DESC
) AS a
LIMIT 0 , 20
UNION ALL SELECT 'other', sum( num ) AS num
FROM (

SELECT `country_name` , count( * ) AS num
FROM `lomo_track_201106`
GROUP BY `country_name`
ORDER BY num DESC
LIMIT 20 , 1000000
) AS b;

表中有无唯一标识的字段，
将
SELECT `country_name` , count( * ) AS num
FROM `lomo_track_201106`
GROUP BY `country_name`
ORDER BY num DESC
存为 VIEW

不想用视图 也不想用存储过程


要求就是 查询出来数量在前二十的国家名称 然后将其他的国家的数量归到other字段里面

首先country_name加索引不需要多讲了。如果不用view的话，
可以考虑使用减法来统计other的count，理论上在country数量较多的时候，会有点优势

SQL code

 SELECT country_name, num FROM
(SELECT country_name, count(*) AS num FROM lomo_track_201106 GROUP BY country_name ORDER BY num DESC LIMIT 20) a
  UNION ALL
 SELECT 'other', b.total - sum(a.num) FROM
(SELECT country_name, count(*) AS num FROM lomo_track_201106 GROUP BY country_name ORDER BY num DESC LIMIT 20) a,
(SELECT count(*) AS total FROM lomo_track_201106) b

因为无条件统计一张表的记录数，这个不需要扫描表或索引的。