====== Oracle function last_day ======
===== SQL Server로 변경 =====
<code sql>
declare @date_t datetime
declare @d datetime
set @date_t = '20200820'
set @d = DATEADD(m, 1, @date_t)
set @d = DATEADD(d, - DAY(@d), @d)
select @date_t, @d
</code>
<code sql>
create or alter function dbo.XF_LAST_DAY(
    @ad_date datetime
) return datetime as
BEGIN
   DECLARE @d datetime
   set @d = DATEADD(m, 1, @ad_date)
   return DATEADD(d, - DAY(@d), @d)
END
</code>