优化SQL语句

SQL code

SELECT   a.co    ,a.c4    ,b.c    ,b.c9    ,c.c9    ,b.c4/b.c9*10000    ,c.c4/c.c9*10000FROM table_1 a RIGHT JOIN (SELECT co,MAX(c1) AS c1,c4,c9 FROM table_2 GROUP BY co )bON a.co=b.co   LEFT JOIN table_2 cON b.co=c.co AND b.c1>c.c1 AND NOT EXISTS(SELECT 1 FROM table_2 WHERE co=b.co AND c1<b.c1 AND c1>c.c1)WHERE YEAR(b.c1)=YEAR(20120331000000) AND QUARTER(b.c1)=QUARTER(20120331000000)    

数据量： 几十万行

[解决办法]
SELECT co,MAX(c1) AS c1,c4,c9 FROM table_2 GROUP BY co

这个全表分组求最大耗时吗
[解决办法]
贴一下你的 show index from a; show index from b; ...
[解决办法]
贴出执行计划show index from a; show index from b;