mysql中像这样的复杂的语句该如何优化？

[phf0313]

SELECT SUM(num) AS probability,COUNT(*) AS `count`,CONVERT(post_time,CHAR(10)) AS `time` FROM fd_projection_logs `logs` WHERE FROM_UNIXTIME(UNIX_TIMESTAMP(post_time),'%H')>=8 AND FROM_UNIXTIME(UNIX_TIMESTAMP(post_time),'%H')<12 AND num>0 GROUP BY CONVERT(post_time,CHAR(10))

上面的这种复杂的语句如何优化？
数据类型：
num int
post_time timestamp

[wwwwb]

在你的WHERE、GROUP中均用到函数，无法用到索引

[Rotel-刘志东]

explain select....列出执行计划。

[ACMAIN_CHM]

create index xxx on fd_projection_logs(num); create index xxx on fd_projection_logs(post_time);