SQL查询使用两个表查找最近的日期

I have two tables in a database. One called Users and one called Days. The Users table has a column called ID which contains some numbers and an ActiveUser column which contains either a 0(not active) or 1(active). The Days table has a column called UserID which contains the same numbers the ID column from the Users table has. It also has a column called Day which contains info like "2015-01-01 00:00:00:000".I have two tables in a database. One called Use