题解 | #广告点击的高峰期#
广告点击的高峰期
https://www.nowcoder.com/practice/6756d65784f9413b8505c1d0c6754b3a
select subString(click_time,12,2) as click_hour, count(subString(click_time,12,2)) as click_cnt from user_ad_click_time a group by subString(click_time,12,2) limit 1
说句实话,这个题有毛病,第二个表有何用?