mysql计算当日注册用户缴费数

Question

现有两张表：
meter表

user表

user表是用户的注册信息，meter表是用户的缴费信息，现在我想查出在注册当日即缴费的用户数量，请问该怎么查，求大神指点。

Answer 1

select count(1) as '当日即缴费的用户数量' from user a
inner join meter b on a.id=b.userId
and DATE_FORMAT(a.time, '%Y-%m-%d')=DATE_FORMAT(b.time, '%Y-%m-%d')

根据业务，如果缴费信息表有注册当天多次缴费，就先去重：
select count(1) as '当日即缴费的用户数量' from user a
inner join (select userId,min(time) as time from meter group by userId) b on a.id=b.userId
and DATE_FORMAT(a.time, '%Y-%m-%d')=DATE_FORMAT(b.time, '%Y-%m-%d')