设定固定时间段：8.2---》8.5
也就是：两个时间段，只要有交集就能筛选出来：
下面的两个sql语句，实现的效果是一样的：
1：$sql="select * from fs_ads where `start_time` <= '$ed' and `end_time` >= '$sd'";
2：
$sql="select * from (
select ads_id,file_id,client_type,client_name,brand,model,cal_type start_time,end_time,
CASE
when (start_time>='$sd') then start_time
when (start_time<'$sd') then '$sd'
end as start1,
CASE
when (end_time>='$ed') then '$ed'
when (end_time<'$ed') then end_time
end as end1
from fs_ads )
a where a.start1<=a.end1;
";
select ads_id,file_id,client_type,client_name,brand,model,cal_type start_time,end_time,
CASE
when (start_time>='$sd') then start_time
when (start_time<'$sd') then '$sd'
end as start1,
CASE
when (end_time>='$ed') then '$ed'
when (end_time<'$ed') then end_time
end as end1
from fs_ads )
a where a.start1<=a.end1;
";
注：$sd,$ed是用户选择的时间