这两个sql如何合并

Question

SELECT from_unixtime(regtime, '%Y%m%d') dt , count(*) num from android_user  group by dt order by dt desc limit 20;

SELECT from_unixtime(regtime, '%Y%m%d') dt , count(*) num from android_user where `parent_id` <> ''  group by dt order by dt desc limit 20;

最后得到一张表，安日期分组，第二张图日期没有的num为0？？
求大神指导

Answer 1

SELECT from_unixtime(regtime, '%Y%m%d') dt , sum(case when parent_id='' then 0 else 1 end) num from android_user group by dt order by dt desc limit 20;

Answer 2

你这个是一张表吧？可以使用一条sql语句呀。
SELECT from_unixtime(regtime, '%Y%m%d') dt , count(*) num from android_user where `parent_id` <> '' group by dt order by dt desc limit 20;